Multiuser transreceiving method in wireless communication system and device for same

ABSTRACT

A method for transmitting data from a station (STA) device in a wireless LAN (WLAN) system, according to one embodiment of the present invention, comprises the steps of: generating a physical protocol data unit (PPDU) including a physical preamble and a data field; and transmitting the PPDU, wherein when the data field is transmitted by using a 106-tone resource unit including first to fourth pilot tones, the positions of the first to the fourth pilot tones may be identical to the positions of four pilot tones from among eight pilot tones included in four 26-tone resource units, which are present at a position corresponding to the 106-tone resource unit, or identical to the positions of four pilot tones from among eight pilot tones included in two 52-tone resource units, which are present at a position corresponding to the 106-tone resource unit.

This application is a continuation of U.S. patent application Ser. No.15/523,275, filed on Apr. 28, 2017, now U.S. Pat. No. 10,200,175, whichis the National Stage filing under 35 U.S.C. 371 of InternationalApplication No. PCT/KR2015/011645, filed on Nov. 2, 2015, which claimsthe benefit of U.S. Provisional Application Nos. 62/073,023, filed onOct. 31, 2014, 62/090,371, filed on Dec. 11, 2014, 62/093,409, filed onDec. 18, 2014, 62/137,236, filed on Mar. 24, 2015, 62/163,349, filed onMay 18, 2015, 62/172,250, filed on Jun. 8, 2015, and 62/175,440, filedon Jun. 15, 2015, the contents of which are all hereby incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more specifically, proposes an efficient tone plan applicable to a newframe and numerology of a future wireless LAN system.

BACKGROUND ART

Wi-Fi is a wireless local area network (WLAN) technology which enables adevice to access the Internet in a frequency band of 2.4 GHz, 5 GHz or60 GHz.

A WLAN is based on the institute of electrical and electronic engineers(IEEE) 802.11 standard. The wireless next generation standing committee(WNG SC) of IEEE 802.11 is an ad-hoc committee which is worried aboutthe next-generation wireless local area network (WLAN) in the medium tolonger term.

IEEE 802.11n has an object of increasing the speed and reliability of anetwork and extending the coverage of a wireless network. Morespecifically, IEEE 802.11n supports a high throughput (HT) providing amaximum data rate of 600 Mbps. Furthermore, in order to minimize atransfer error and to optimize a data rate, IEEE 802.11n is based on amultiple inputs and multiple outputs (MIMO) technology in which multipleantennas are used at both ends of a transmission unit and a receptionunit.

As the spread of a WLAN is activated and applications using the WLAN arediversified, in the next-generation WLAN system supporting a very highthroughput (VHT), IEEE 802.11ac has been newly enacted as the nextversion of an IEEE 802.11n WLAN system. IEEE 802.11ac supports a datarate of 1 Gbps or more through 80 MHz bandwidth transmission and/orhigher bandwidth transmission (e.g., 160 MHz), and chiefly operates in a5 GHz band.

Recently, a need for a new WLAN system for supporting a higherthroughput than a data rate supported by IEEE 802.11ac comes to thefore.

The scope of IEEE 802.11ax chiefly discussed in the next-generation WLANtask group called a so-called IEEE 802.11ax or high efficiency (HEW)WLAN includes 1) the improvement of an 802.11 physical (PHY) layer andmedium access control (MAC) layer in bands of 2.4 GHz, 5 GHz, etc., 2)the improvement of spectrum efficiency and area throughput, 3) theimprovement of performance in actual indoor and outdoor environments,such as an environment in which an interference source is present, adense heterogeneous network environment, and an environment in which ahigh user load is present and so on.

A scenario chiefly taken into consideration in IEEE 802.11ax is a denseenvironment in which many access points (APs) and many stations (STAs)are present. In IEEE 802.11ax, the improvement of spectrum efficiencyand area throughput is discussed in such a situation. More specifically,there is an interest in the improvement of substantial performance inoutdoor environments not greatly taken into consideration in existingWLANs in addition to indoor environments.

In IEEE 802.11ax, there is a great interest in scenarios, such aswireless offices, smart homes, stadiums, hotspots, andbuildings/apartments. The improvement of system performance in a denseenvironment in which many APs and many STAs are present is discussedbased on the corresponding scenarios.

In the future, it is expected in IEEE 802.11ax that the improvement ofsystem performance in an overlapping basic service set (OBSS)environment, the improvement of an outdoor environment, cellularoffloading, and so on rather than single link performance improvement ina single basic service set (BSS) will be actively discussed. Thedirectivity of such IEEE 802.11ax means that the next-generation WLANwill have a technical scope gradually similar to that of mobilecommunication. Recently, when considering a situation in which mobilecommunication and a WLAN technology are discussed together in smallcells and direct-to-direct (D2D) communication coverage, it is expectedthat the technological and business convergence of the next-generationWLAN based on IEEE 802.11ax and mobile communication will be furtheractivated.

DISCLOSURE Technical Problem

When an FFT size quadruple that of the legacy WLAN system is used in an802.11ax system, it is difficult to apply pilot deployment of an802.11ac system. Accordingly, the present invention supplements andextends the tone plan proposed in 802.11n and 802.11ac systems topropose an efficient pilot design method suitable for numerology of an802.11ax system.

Technical Solution

A data transmission method of a station (STA) in a wireless LAN (WLAN)system according to an embodiment of the present invention includes:generating a physical protocol data unit (PPDU) including a physicalpreamble and a data field; and transmitting the PPDU, wherein, when thedata field is transmitted using a 106-tone resource unit including firstto fourth pilot tones, positions of the first to fourth pilot tonescorrespond to positions of 4 pilot tones from among 8 pilot tonesincluded in 4 26-tone resource units at positions corresponding to the106-tone resource unit or correspond to positions of 4 pilot tones fromamong 8 pilot tones included in 2 52-tone resource units at positionscorresponding to the 106-tone resource unit.

The 4 26-tone resource units and 2 leftover tones may be present at thepositions corresponding to the 106-tone resource unit, the 2 leftovertones being positioned between second and third 26-tone resource unitsfrom among the 4 26-tone resource units sequentially positioned, orwherein the 2 26-tone resource units and 2 leftover tones may be presentat the positions corresponding to the 106-tone resource unit, the 2leftover tones being positioned between the 2 26-tone resource unitssequentially positioned.

The position of the first pilot tone may correspond to a position of oneof 2 pilot tones included in the first 26-tone resource unit, theposition of the second pilot tone may correspond to a position of one of2 pilot tones included in the second 26-tone resource unit, the positionof the third pilot tones may correspond to a position of one of 2 pilottones included in the third 26-tone resource unit, and the position ofthe fourth pilot tones may correspond to a position of one of 2 pilottones included in the fourth 26-tone resource unit.

The position of the first pilot tone may correspond to a position of oneof the 2 pilot tones included in the first 26-tone resource unit, whichis a longer distance from the 2 leftover tones, the position of thesecond pilot tone may correspond to a position of one of the 2 pilottones included in the second 26-tone resource unit, which is a longerdistance from the 2 leftover tones, the position of the third pilot tonemay correspond to a position of one of the 2 pilot tones included in thethird 26-tone resource unit, which is a longer distance from the 2leftover tones, and the position of the fourth pilot tone may correspondto a position of one of the 2 pilot tones included in the fourth 26-toneresource unit, which is a longer distance from the 2 leftover tones.

When 26 tones included in each 26-tone resource unit are sequentiallypositioned at indices 0 to 25, 2 pilot tones included in each 26-toneresource unit may be respectively positioned at the indices 6 and 20.

The position of the first pilot tone may correspond to a position of oneof the 2 pilot tones included in the first 26-tone resource unit, whichis positioned at the index 6, the position of the second pilot tone maycorrespond to a position of one of the 2 pilot tones included in thesecond 26-tone resource unit, which is positioned at the index 6, theposition of the third pilot tone may correspond to a position of one ofthe 2 pilot tones included in the third 26-tone resource unit, which ispositioned at the index 20, and the position of the fourth pilot tonemay correspond to a position of one of the 2 pilot tones included in thefourth 26-tone resource unit, which is positioned at the index 20.

When 106 tones included in the 106-tone resource unit are sequentiallypositioned at indices 0 to 105, the first pilot tone may be positionedat the index 6, the second pilot tone may be positioned at the index 32,the third pilot tone may be positioned at the index 74, and the fourthpilot tone may be positioned at the index 100.

An STA in a WLAN system according to another embodiment of the presentinvention includes an RF unit for transmitting and receiving RF signalsand a processor for controlling the RF unit, wherein the processor isconfigured to generate a physical protocol data unit (PPDU) including aphysical preamble and a data field and to transmit the PPDU, wherein,when the data field is transmitted using a 106-tone resource unitincluding first to fourth pilot tones, positions of the first to fourthpilot tones correspond to positions of 4 pilot tones from among 8 pilottones included in 4 26-tone resource units at positions corresponding tothe 106-tone resource unit or correspond to positions of 4 pilot tonesfrom among 8 pilot tones included in 2 52-tone resource units atpositions corresponding to the 106-tone resource unit.

The 4 26-tone resource units and 2 leftover tones may be present at thepositions corresponding to the 106-tone resource unit, the 2 leftovertones being positioned between second and third 26-tone resource unitsfrom among the 4 26-tone resource units sequentially positioned, orwherein the 2 26-tone resource units and 2 leftover tones may be presentat the positions corresponding to the 106-tone resource unit, the 2leftover tones being positioned between the 2 26-tone resource unitssequentially positioned.

The position of the first pilot tone may correspond to a position of oneof 2 pilot tones included in the first 26-tone resource unit, theposition of the second pilot tone may correspond to a position of one of2 pilot tones included in the second 26-tone resource unit, the positionof the third pilot tones may correspond to a position of one of 2 pilottones included in the third 26-tone resource unit, and the position ofthe fourth pilot tones may correspond to a position of one of 2 pilottones included in the fourth 26-tone resource unit.

The position of the first pilot tone may correspond to a position of oneof the 2 pilot tones included in the first 26-tone resource unit, whichis a longer distance from the 2 leftover tones, the position of thesecond pilot tone may correspond to a position of one of the 2 pilottones included in the second 26-tone resource unit, which is a longerdistance from the 2 leftover tones, the position of the third pilot tonemay correspond to a position of one of the 2 pilot tones included in thethird 26-tone resource unit, which is a longer distance from the 2leftover tones, and the position of the fourth pilot tone may correspondto a position of one of the 2 pilot tones included in the fourth 26-toneresource unit, which is a longer distance from the 2 leftover tones.

When 26 tones included in each 26-tone resource unit are sequentiallypositioned at indices 0 to 25, 2 pilot tones included in each 26-toneresource unit may be respectively positioned at the indices 6 and 20.

The position of the first pilot tone may correspond to a position of oneof the 2 pilot tones included in the first 26-tone resource unit, whichis positioned at the index 6, the position of the second pilot tone maycorrespond to a position of one of the 2 pilot tones included in thesecond 26-tone resource unit, which is positioned at the index 6, theposition of the third pilot tone may correspond to a position of one ofthe 2 pilot tones included in the third 26-tone resource unit, which ispositioned at the index 20, and the position of the fourth pilot tonemay correspond to a position of one of the 2 pilot tones included in thefourth 26-tone resource unit, which is positioned at the index 20.

When 106 tones included in the 106-tone resource unit are sequentiallypositioned at indices 0 to 105, the first pilot tone may be positionedat the index 6, the second pilot tone may be positioned at the index 32,the third pilot tone may be positioned at the index74 , and the fourthpilot tone may be positioned at the index 100.

Advantageous Effects

The present invention can reduce overhead of preambles and PLOP headersof the legacy WLAN system and design an efficient PPDU transmissionstructure to improve system efficiency. Specifically, the presentinvention supplements and extends the multi-stream pilot design methodproposed in IEEE 802.11n to propose an efficient pilot design methodapplicable to a new frame structure and numerology of a future WLANsystem.

Various effects of the present invention will be described in detailbelow with reference to the attached drawings.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an example of an IEEE 802.11 system to whichthe present invention may be applied;

FIG. 2 is a diagram illustrating the structure of a layer architectureof an IEEE 802.11 system to which the present invention may be applied;

FIG. 3 illustrates a non-HT format PPDU and an HT format PPDU in awireless communication system to which the present invention may beapplied;

FIG. 4 illustrates a VHT format PPDU in a wireless communication systemto which the present invention may be applied;

FIG. 5 illustrates constellation diagrams for classifying a PPDU formatin a wireless communication system to which the present invention may beapplied;

FIG. 6 illustrates a MAC frame format in an IEEE 802.11 system to whichthe present invention may be applied;

FIG. 7 illustrates an HT format of an HT control field in a wirelesscommunication system to which the present invention may be applied;

FIG. 8 illustrates a VHT format of the HT control field in a wirelesscommunication system to which the present invention may be applied;

FIG. 9 is a diagram illustrating a normal link setup procedure in awireless communication system to which the present invention may beapplied;

FIG. 10 is a diagram illustrating a random backoff period and a frametransmission procedure in a wireless communication system to which thepresent invention may be applied;

FIGS. 11 to 14 are diagrams illustrating a high efficiency (HE) formatPPDU according to an embodiment of the present invention;

FIGS. 15 to 17 are diagrams illustrating a resource allocation unit inan OFDMA multi-user transmission method according to an embodiment ofthe present invention;

FIG. 16 illustrates a case in which a PPDU bandwidth is 40 MHz;

FIG. 17 illustrates a case in which a PPDU bandwidth is 80 MHz;

FIG. 18 is a diagram illustrating pilot tone plans of legacy systems;

FIGS. 19 to 22 are tables showing values of pilot tones depending onnumber of streams according to an embodiment of the present invention;

FIG. 23 is a table showing sequence groups for generating pilot valuesaccording to an embodiment of the present invention;

FIGS. 24 and 25 are tables showing values of pilot tones depending onnumber of streams according to an embodiment of the present invention;

FIGS. 26 and 27 are tables showing values of pilot tones depending onnumber of streams according to an embodiment of the present invention;

FIG. 28 is a table showing sequence groups for generating pilot valuesaccording to an embodiment of the present invention;

FIGS. 29 and 30 are tables showing values of pilot tones depending onnumber of streams according to an embodiment of the present invention;

FIG. 31 is a table showing sequence groups for generating pilot valuesaccording to an embodiment of the present invention;

FIG. 32 is a diagram illustrating positions of pilot tones included in106 tone resource units;

FIG. 33 is tables showing values of pilot tones allocated per STAaccording to an embodiment of the present invention; and

FIG. 34 is a flowchart illustrating a data transmission method of an STAdevice according to an embodiment of the present invention.

FIG. 35 is a block diagram of each STA device according to an embodimentof the present invention.

BEST MODES

The terms used in this specification were selected to include current,widely-used, general terms, in consideration of the functions of thepresent invention. However, the terms may represent different meaningsaccording to the intentions of the skilled person in the art oraccording to customary usage, the appearance of new technology, etc. Incertain cases, a term may be one that was arbitrarily established by theapplicant. In such cases, the meaning of the term will be defined in therelevant portion of the detailed description. As such, the terms used inthe specification are not to be defined simply by the name of the termsbut are to be defined based on the meanings of the terms as well as theoverall description of the present invention.

In addition, embodiments will be described in detail with reference tothe accompanying drawings and contents illustrated in the accompanyingdrawings, but the present invention is not limited by the embodiments.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

The following technologies may be used in a variety of wirelesscommunication systems, such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), and non-orthogonalmultiple access (NOMA). CDMA may be implemented using a radiotechnology, such as universal terrestrial radio access (UTRA) orCDMA2000. TDMA may be implemented using a radio technology, such asglobal system for Mobile communications (GSM)/general packet radioservice (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA maybe implemented using a radio technology, such as institute of electricaland electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, or evolved UTRA (E-UTRA). UTRA is part of a universalmobile telecommunications system (UMTS). 3rd generation partnershipproject (3GPP) long term evolution (LTE) is part of an evolved UMTS(E-UMTS) using evolved UMTS terrestrial radio access (E-UTRA), and itadopts OFDMA in downlink and adopts SC-FDMA in uplink. LTE-advanced(LTE-A) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, thatis, radio access systems. That is, steps or portions that belong to theembodiments of the present invention and that are not described in orderto clearly expose the technical spirit of the present invention may besupported by the documents. Furthermore, all terms disclosed in thisdocument may be described by the standard documents.

In order to more clarify a description, 3GPP LTE/LTE-A is chieflydescribed, but the technical characteristics of the present inventionare not limited thereto.

General System

FIG. 1 is a diagram showing an example of an IEEE 802.11 system to whichan embodiment of the present invention may be applied.

The IEEE 802.11 configuration may include a plurality of elements. Theremay be provided a wireless communication system supporting transparentstation (STA) mobility for a higher layer through an interaction betweenthe elements. A basic service set (BSS) may correspond to a basicconfiguration block in an IEEE 802.11 system.

FIG. 1 illustrates that three BSSs BSS 1 to BSS 3 are present and twoSTAs (e.g., an STA 1 and an STA 2 are included in the BSS 1, an STA 3and an STA 4 are included in the BSS 2, and an STA 5 and an STA 6 areincluded in the BSS 3) are included as the members of each BSS.

In FIG. 1, an ellipse indicative of a BSS may be interpreted as beingindicative of a coverage area in which STAs included in thecorresponding BSS maintain communication. Such an area may be called abasic service area (BSA). When an STA moves outside the BSA, it isunable to directly communicate with other STAs within the correspondingBSA.

In the IEEE 802.11 system, the most basic type of a BSS is anindependent a BSS (IBSS). For example, an IBSS may have a minimum formincluding only two STAs. Furthermore, the BSS 3 of FIG. 1 which is thesimplest form and from which other elements have been omitted maycorrespond to a representative example of the IBSS. Such a configurationmay be possible if STAs can directly communicate with each other.Furthermore, a LAN of such a form is not previously planned andconfigured, but may be configured when it is necessary. This may also becalled an ad-hoc network.

When an STA is powered off or on or an STA enters into or exits from aBSS area, the membership of the STA in the BSS may be dynamicallychanged. In order to become a member of a BSS, an STA may join the BSSusing a synchronization process. In order to access all of services in aBSS-based configuration, an STA needs to be associated with the BSS.Such association may be dynamically configured, and may include the useof a distribution system service (DSS).

In an 802.11 system, the distance of a direct STA-to-STA may beconstrained by physical layer (PHY) performance. In any case, the limitof such a distance may be sufficient, but communication between STAs ina longer distance may be required, if necessary. In order to supportextended coverage, a distribution system (DS) may be configured.

The DS means a configuration in which BSSs are interconnected. Morespecifically, a BSS may be present as an element of an extended form ofa network including a plurality of BSSs instead of an independent BSS asin FIG. 1.

The DS is a logical concept and may be specified by the characteristicsof a distribution system medium (DSM). In the IEEE 802.11 standard, awireless medium (WM) and a distribution system medium (DSM) arelogically divided. Each logical medium is used for a different purposeand used by a different element. In the definition of the IEEE 802.11standard, such media are not limited to the same one and are also notlimited to different ones. The flexibility of the configuration (i.e., aDS configuration or another network configuration) of an IEEE 802.11system may be described in that a plurality of media is logicallydifferent as described above. That is, an IEEE 802.11 systemconfiguration may be implemented in various ways, and a correspondingsystem configuration may be independently specified by the physicalcharacteristics of each implementation example.

The DS can support a mobile device by providing the seamless integrationof a plurality of BSSs and providing logical services required to handlean address to a destination.

An AP means an entity which enables access to a DS through a WM withrespect to associated STAs and has the STA functionality. The movementof data between a BSS and the DS can be performed through an AP. Forexample, each of the STA 2 and the STA 3 of FIG. 1 has the functionalityof an STA and provides a function which enables associated STAs (e.g.,the STA 1 and the STA 4) to access the DS. Furthermore, all of APsbasically correspond to an STA, and thus all of the APs are entitiescapable of being addressed. An address used by an AP for communicationon a WM and an address used by an AP for communication on a DSM may notneed to be necessarily the same.

Data transmitted from one of STAs, associated with an AP, to the STAaddress of the AP may be always received by an uncontrolled port andprocessed by an IEEE 802.1X port access entity. Furthermore, when acontrolled port is authenticated, transmission data (or frame) may bedelivered to a DS.

A wireless network having an arbitrary size and complexity may include aDS and BSSs. In an IEEE 802.11 system, a network of such a method iscalled an extended service set (ESS) network. The ESS may correspond toa set of BSSs connected to a single DS. However, the ESS does notinclude a DS. The ESS network is characterized in that it looks like anIBSS network in a logical link control (LLC) layer. STAs included in theESS may communicate with each other. Mobile STAs may move from one BSSto the other BSS (within the same ESS) in a manner transparent to theLLC layer.

In an IEEE 802.11 system, the relative physical positions of BSSs inFIG. 1 are not assumed, and the following forms are all possible.

More specifically, BSSs may partially overlap, which is a form commonlyused to provide consecutive coverage. Furthermore, BSSs may not bephysically connected, and logically there is no limit to the distancebetween BSSs. Furthermore, BSSs may be placed in the same positionphysically and may be used to provide redundancy. Furthermore, one (orone or more) IBSS or ESS networks may be physically present in the samespace as one or more ESS networks. This may correspond to an ESS networkform if an ad-hoc network operates at the position in which an ESSnetwork is present, if IEEE 802.11 networks that physically overlap areconfigured by different organizations, or if two or more differentaccess and security policies are required at the same position.

In a WLAN system, an STA is an apparatus operating in accordance withthe medium access control (MAC)/PHY regulations of IEEE 802.11. An STAmay include an AP STA and a non-AP STA unless the functionality of theSTA is not individually different from that of an AP. In this case,assuming that communication is performed between an STA and an AP, theSTA may be interpreted as being a non-AP STA. In the example of FIG. 1,the STA 1, the STA 4, the STA 5, and the STA 6 correspond to non-APSTAs, and the STA 2 and the STA 3 correspond to AP STAs.

A non-AP STA corresponds to an apparatus directly handled by a user,such as a laptop computer or a mobile phone. In the followingdescription, a non-AP STA may also be called a wireless device, aterminal, user equipment (UE), a mobile station (MS), a mobile terminal,a wireless terminal, a wireless transmit/receive unit (WTRU), a networkinterface device, a machine-type communication (MTC) device, amachine-to-machine (M2M) device or the like.

Furthermore, an AP is a concept corresponding to a base station (BS), anode-B, an evolved Node-B (eNB), a base transceiver system (BTS), afemto BS or the like in other wireless communication fields.

Hereinafter, in this specification, downlink (DL) means communicationfrom an AP to a non-AP STA. Uplink (UL) means communication from anon-AP STA to an AP. In DL, a transmitter may be part of an AP, and areceiver may be part of a non-AP STA. In UL, a transmitter may be partof a non-AP STA, and a receiver may be part of an AP.

FIG. 2 is a diagram illustrating the structure of a layer architectureof an IEEE 802.11 system to which an embodiment of the present inventionmay be applied.

Referring to FIG. 2, the layer architecture of an IEEE 802.11 system mayinclude a medium access control (MAC) sublayer/layer and a physical(PHY) sublayer/layer.

PHY may be divided into a physical layer convergence procedure (PLOP)entity and a physical medium dependent (PMD) entity. In this case, thePLOP entity connects MAC and data frames and the PMD entity wirelesslytransmits/receives data to/from two or more STAs.

Both MAC and PHY may include management entities which may berespectively called a MAC sublayer management entity (MLME) and aphysical sublayer management entity (PLME). Such management entitiesprovide a layer management service interface through operation of alayer management function. The MLME may be connected to the PLME andperform MAC management operation and the PLME may be connected to theMLME and perform PHY management operation.

In order to provide a precise MAC operation, a station management entity(SME) may be present in each STA. The SME is a management entityindependent of each layer, and collects layer-based state informationfrom the MLME and the PLME or sets the values of layer-specificparameters. The SME may perform such a function instead of common systemmanagement entities and may implement a standard management protocol.

The MLME, the PLME, and the SME may interact with each other usingvarious methods based on primitives. More specifically, anXX-GET.request primitive is used to request the value of a managementinformation base (MIB) attribute. An XX-GET.confirm primitive returnsthe value of a corresponding MIB attribute if the state is “SUCCESS”,and indicates an error in the state field and returns the value in othercases. An XX-SET.request primitive is used to make a request so that adesignated MIB attribute is set as a given value. If an MIB attributemeans a specific operation, such a request requests the execution of thespecific operation. Furthermore, an XX-SET.confirm primitive means thata designated MIB attribute has been set as a requested value if thestate is “SUCCESS.” In other cases, the XX-SET.confirm primitiveindicates that the state field is an error situation. If an MIBattribute means a specific operation, the primitive may confirm that acorresponding operation has been performed.

PHY provides an interface to MAC through TXVECTOR, RXVECTOR andPHYCONFIG_VECTOR. TXVECTOR supports a transmission parameter per PPDUfor PHY. PHY notifies MAC of a received PPDU parameter using RXVECTOR.TXVECTOR is delivered from MAC to PHY through PHY-TXSTART.requestprimitive and RXVECTOR is delivered from PHY to MAC throughPHY-RXSTART.indication premitive.

MAC sets operation of PHY using PHYCONFIG_VECTOR irrespective of frametransmission or reception.

Operation of each sublayer (or layer) will be briefly described.

MAC attaches a MAC header and a frame check sequence (FCS) to a MACservice data unit (MSDU) received from a higher layer (e.g., LLC) or afragment of the MSDU to generate one or more MAC protocol data units(MPDUs). The generated MPDUs are delivered to PHY.

When an aggregated MSDU (A-MSDU) scheme is used, a plurality of MSDUsmay be aggregated into a single A-MSDU. MSDU aggregation may beperformed in a layer higher than MAC. A-MSDU is delivered to PHY as asingle MPDU (when the MPDU is not fragmented).

PHY attaches an additional field including information necessary for aphysical layer transceiver to a physical service data unit (PSDU)received from MAC to generate a physical protocol data unit (PPDU). ThePPDU is transmitted through a radio medium.

Since the PSDU is received by PHY from MAC and the MPDU is transmittedfrom MAC to PHY, the PSDU is substantially the same as the MPDU.

When an aggregated MPDU (A-MPDU) scheme is used, a plurality of MPDUs(here, each MPDU may carry A-MSDU) may be aggregated into a singleA-MPDU. MPDU aggregation may be performed in a layer lower than MAC.A-MPDU may be obtained by aggregating various types of MPDUs (e.g., QoSdata, ACK (Acknowledge), block ACK, etc.). PHY receives the A-MPDU fromMAC as a single PSDU. That is, a PSDU is composed of a plurality ofMPDUs. Accordingly, the A-MPDU is transmitted in a single PPDU through aradio medium.

Physical Protocol Data Unit (PPDU) Format

A PPDU means a data block generated in the physical layer. A PPDU formatis described below based on an IEEE 802.11 a WLAN system to which anembodiment of the present invention may be applied.

FIG. 3 illustrates a non-HT format PPDU and an HT format PPDU in awireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 3(a) illustrates a non-HT format PPDU for supporting IEEE 802.11a/gsystems. The non-HT PPDU may also be called a legacy PPDU.

Referring to FIG. 3(a), the non-HT format PPDU is configured to includea legacy format preamble, including a legacy (or non-HT) short trainingfield (L-STF), a legacy (or non-HT) long training field (L-LTF), and alegacy (or non-HT) signal (L-SIG) field, and a data field.

The L-STF may include a short training orthogonal frequency divisionmultiplexing symbol (OFDM). The L-STF may be used for frame timingacquisition, automatic gain control (AGC), diversity detection, andcoarse frequency/time synchronization.

The L-LTF may include a long training OFDM symbol. The L-LTF may be usedfor fine frequency/time synchronization and channel estimation.

The L-SIG field may be used to send control information for thedemodulation and decoding of the data field. The L-SIG field may includeinformation on a data rate and data length

FIG. 3(b) illustrates an HT mixed format PPDU for supporting both anIEEE 802.11n system and IEEE 802.11a/g system.

Referring to FIG. 3(b), the HT mixed format PPDU is configured toinclude a legacy format preamble including an L-STF, an L-LTF, and anL-SIG field, an HT format preamble including an HT-signal (HT-SIG)field, a HT short training field (HT-STF), and a HT long training field(HT-LTF), and a data field.

The L-STF, the L-LTF, and the L-SIG field mean legacy fields forbackward compatibility and are the same as those of the non-HT formatfrom the L-STF to the L-SIG field. An L-STA may interpret a data fieldthrough an L-LTF, an L-LTF, and an L-SIG field although it receives anHT mixed PPDU. In this case, the L-LTF may further include informationfor channel estimation to be performed by an HT-STA in order to receivethe HT mixed PPDU and to demodulate the L-SIG field and the HT-SIGfield.

An HT-STA may be aware of an HT mixed format PPDU using the HT-SIG fieldsubsequent to the legacy fields, and may decode the data field based onthe HT mixed format PPDU.

The HT-LTF may be used for channel estimation for the demodulation ofthe data field. IEEE 802.11n supports single user multi-input andmulti-output (SU-MIMO) and thus may include a plurality of HT-LTFs forchannel estimation with respect to each of data fields transmitted in aplurality of spatial streams.

The HT-LTF may include a data HT-LTF used for channel estimation for aspatial stream and an extension HT-LTF additionally used for fullchannel sounding. Accordingly, a plurality of HT-LTFs may be the same asor greater than the number of transmitted spatial streams.

In the HT mixed format PPDU, the L-STF, the L-LTF, and the L-SIG fieldsare first transmitted so that an L-STA can receive the L-STF, the L-LTF,and the L-SIG fields and obtain data. Thereafter, the HT-SIG field istransmitted for the demodulation and decoding of data transmitted for anHT-STA.

An L-STF, an L-LTF, L-SIG, and HT-SIG fields are transmitted withoutperforming beamforming up to an HT-SIG field so that an L-STA and anHT-STA can receive a corresponding PPDU and obtain data. In an HT-STF,an HT-LTF, and a data field that are subsequently transmitted, radiosignals are transmitted through precoding. In this case, an HT-STF istransmitted so that an STA receiving a corresponding PPDU by performingprecoding may take into considerate a portion whose power is varied byprecoding, and a plurality of HT-LTFs and a data field are subsequentlytransmitted.

FIG. 3(c) illustrates an HT-green field format PPDU (HT-GF format PPDU)for supporting only an IEEE 802.11n system.

Referring to FIG. 3(c), the HT-GF format PPDU includes an HT-GF-STF, anHT-LTF1, an HT-SIG field, a plurality of HT-LTF2s, and a data field.

The HT-GF-STF is used for frame timing acquisition and AGC.

The HT-LTF1 is used for channel estimation.

The HT-SIG field is used for the demodulation and decoding of the datafield.

The HT-LTF2 is used for channel estimation for the demodulation of thedata field. Likewise, an HT-STA uses SU-MIMO. Accordingly, a pluralityof the HT-LTF2s may be configured because channel estimation isnecessary for each of data fields transmitted in a plurality of spatialstreams.

The plurality of HT-LTF2s may include a plurality of data HT-LTFs and aplurality of extension HT-LTFs like the HT-LTF of the HT mixed PPDU.

In FIGS. 3(a) to 3(c), the data field is a payload and may include aservice field, a scrambled PSDU (PSDU) field, tail bits, and paddingbits. All of the bits of the data field are scrambled.

FIG. 3(d) illustrates a service field included in the data field. Theservice field has 16 bits. The 16 bits are assigned No. 0 to No. 15 andare sequentially transmitted from the No. 0 bit. The No. 0 bit to theNo. 6 bit are set to 0 and are used to synchronize a descrambler withina reception stage.

An IEEE 802.11ac WLAN system supports the transmission of a DLmulti-user multiple input multiple output (MU-MIMO) method in which aplurality of STAs accesses a channel at the same time in order toefficiently use a radio channel. In accordance with the MU-MIMOtransmission method, an AP may simultaneously transmit a packet to oneor more STAs that have been subjected to MIMO pairing.

Downlink multi-user transmission (DL MU transmission) means a technologyin which an AP transmits a PPDU to a plurality of non-AP STAs throughthe same time resources using one or more antennas.

Hereinafter, an MU PPDU means a PPDU which delivers one or more PSDUsfor one or more STAs using the MU-MIMO technology or the OFDMAtechnology. Furthermore, an SU PPDU means a PPDU having a format inwhich only one PSDU can be delivered or which does not have a PSDU.

For MU-MIMO transmission, the size of control information transmitted toan STA may be relatively larger than the size of 802.11n controlinformation. Control information additionally required to supportMU-MIMO may include information indicating the number of spatial streamsreceived by each STA and information related to the modulation andcoding of data transmitted to each STA may correspond to the controlinformation, for example.

Accordingly, when MU-MIMO transmission is performed to provide aplurality of STAs with a data service at the same time, the size oftransmitted control information may be increased according to the numberof STAs which receive the control information.

In order to efficiently transmit the control information whose size isincreased as described above, a plurality of pieces of controlinformation required for MU-MIMO transmission may be divided into twotypes of control information: common control information that isrequired for all of STAs in common and dedicated control informationindividually required for a specific STA, and may be transmitted.

FIG. 4 illustrates a VHT format PPDU in a wireless communication systemto which an embodiment of the present invention may be applied.

FIG. 4 illustrates a VHT format PPDU for supporting an IEEE 802.11acsystem.

Referring to FIG. 4, the VHT format PPDU is configured to include alegacy format preamble including an L-STF, an L-LTF, and an L-SIG field,a VHT format preamble including a VHT-signal-A (VHT-SIG-A) field, a VHTshort training field (VHT-STF), a VHT long training field (VHT-LTF), anda VHT-signal-B (VHT-SIG-B) field, and a data field.

The L-STF, the L-LTF, and the L-SIG field mean legacy fields forbackward compatibility and have the same formats as those of the non-HTformat. In this case, the L-LTF may further include information forchannel estimation which will be performed in order to demodulate theL-SIG field and the VHT-SIG-A field.

The L-STF, the L-LTF, the L-SIG field, and the VHT-SIG-A field may berepeated in a 20 MHz channel unit and transmitted. For example, when aPPDU is transmitted through four 20 MHz channels (i.e., an 80 MHzbandwidth), the L-STF, the L-LTF, the L-SIG field, and the VHT-SIG-Afield may be repeated every 20 MHz channel and transmitted.

A VHT-STA may be aware of the VHT format PPDU using the VHT-SIG-A fieldsubsequent to the legacy fields, and may decode the data field based onthe VHT-SIG-A field.

In the VHT format PPDU, the L-STF, the L-LTF, and the L-SIG field arefirst transmitted so that even an L-STA can receive the VHT format PPDUand obtain data. Thereafter, the VHT-SIG-A field is transmitted for thedemodulation and decoding of data transmitted for a VHT-STA.

The VHT-SIG-A field is a field for the transmission of controlinformation that is common to a VHT STAs that are MIMO-paired with anAP, and includes control information for interpreting the received VHTformat PPDU.

The VHT-SIG-A field may include a VHT-SIG-A1 field and a VHT-SIG-A 2field.

The VHT-SIG-A1 field may include information about a channel bandwidth(BW) used, information about whether space time block coding (STBC) isapplied or not, a group identifier (ID) for indicating a group ofgrouped STAs in MU-MIMO, information about the number of streams used(the number of space-time streams (NSTS)/part association identifier(AID), and transmit power save forbidden information. In this case, thegroup ID means an identifier assigned to a target transmission STA groupin order to support MU-MIMO transmission, and may indicate whether thepresent MIMO transmission method is MU-MIMO or SU-MIMO.

Table 1 illustrates the VHT-SIG-A1 field.

TABLE 1 Field Bit Description BW 2 Set to “0” if a BW is 20 MHz Set to“1” if a BW is 40 MHz Set to “2” if a BW is 80 MHz Set to “3” if a BW is160 MHz or 80 + 80 MHz Reserved 1 STBC 1 In the case of a VHT SU PPDU:Set to “1” if STBC is used Set to “0” if not In the case of a VHT MUPPDU: Set to “0” group ID 6 Indicate a group ID “0” or “63” indicates aVHT SU PPDU, but indicates a VHT MU PPDU if not NSTS/Partial 12 In thecase of a VHT MU PPDU, divide into 4 user AID positions “p” each havingthree bits “0” if a space-time stream is 0 “1” if a space-time stream is1 “2” if a space-time stream is 2 “3” if a space-time stream is 3 “4” ifa space-time stream is 4 In the case of a VHT SU PPDU, Upper 3 bits areset as follows: “0” if a space-time stream is 1 “1” if a space-timestream is 2 “2” if a space-time stream is 3 “3” if a space-time streamis 4 “4” if a space-time stream is 5 “5” if a space-time stream is 6 “6”if a space-time stream is 7 “7” if a space-time stream is 8 Lower 9 bitsindicate a partial AID. TXOP_PS_NOT_ALLOWED 1 Set to “0” if a VHT APpermits a non-AP VHT STA to switch to power save mode duringtransmission opportunity (TXOP) Set to “1” if not In the case of a VHTPPDU transmitted by a non-AP VHT STA Set to “1” Reserved 1

The VHT-SIG-A2 field may include information about whether a short guardinterval (GI) is used or not, forward error correction (FEC)information, information about a modulation and coding scheme (MCS) fora single user, information about the type of channel coding for multipleusers, beamforming-related information, redundancy bits for cyclicredundancy checking (CRC), the tail bits of a convolutional decoder andso on.

Table 3 illustrates the VHT-SIG-A2 field.

TABLE 3 Field Bit Description Short GI 1 Set to “0” if a short GI is notused in a data field Set to “1” if a short GI is used in a data fieldShort GI 1 Set to “1” if a short GI is used and an extra symboldisambiguation is required for the payload of a PPDU Set to “0” if anextra symbol is not required SU/MU coding 1 In the case of a VHT SUPPDU: Set to “0” in the case of binary convolutional code (BCC) Set to“1” in the case of low-density parity check (LDPC) In the case of a VHTMU PPDU: Indicate coding used if the NSTS field of a user whose userposition is “0” is not “0” Set to “0” in the case of BCC Set to “1” inthe case of PDPC Set to “1” as a reserved field if the NSTS field of auser whose user position is “0” is “0” LDPC Extra 1 Set to “1” if anextra OFDM symbol is required due OFDM symbol to an PDPC PPDU encodingprocedure (in the case of a SU PPDU) or the PPDU encoding procedure ofat least one PDPC user (in the case of a VHT MU PPDU) Set to “0” if notSU VHT 4 In the case of a VHT SU PPDU: MCS/MU Indicate a VHT-MCS indexcoding In the case of a VHT MU PPDU: Indicate coding for user positions“1” to “3” sequentially from upper bits Indicate coding used if the NSTSfield of each user is not “1” Set to “0” in the case of BCC Set to “1”in the case of LDPC Set to “1” as a reserved field if the NSTS field ofeach user is “0” Beamformed 1 In the case of a VHT SU PPDU: Set to “1”if a beamforming steering matrix is applied to SU transmission Set to“0” if not In the case of a VHT MU PPDU: Set to “1” as a reserved fieldReserved 1 CRC 8 Include CRS for detecting an error of a PPDU on thereceiver side Tail 6 Used to terminate the trellis of a convolutionaldecoder Set to “0”

The VHT-STF is used to improve AGC estimation performance in MIMOtransmission.

VHT-STF field duration is 4 μs. A frequency domain sequence used toconfigure the VHT-STF in a transmission bandwidth of 20 MHz may be thesame as that of the L-STF. The VHT-STF in transmission bandwidths of 40MHz/80 MHz may be configured by duplicating a frequency domain sequencein a transmission bandwidth of 20 MHz in units of 20 MHz and performingphase rotation in units of the duplicated 20 MHz.

The VHT-LTF is used for a VHT-STA to estimate MIMO channels. Since a VHTWLAN system supports MU-MIMO, as many VHT-LTFs as the number of spatialstreams in which PPDUs are transmitted may be configured. Additionally,when full channel sounding is supported, the number of VHT-LTFs mayincrease.

The VHT-SIG-B field includes dedicated control information necessary fora plurality of MU-MIMO paired VHT-STAs to receive PPDUs and obtain data.Accordingly, VHT-STAs may be designed to decode the VHT-SIG-B field onlywhen common control information included in the VHT-SIG-A fieldindicates that a currently received PPDU is for MU-MIMO transmission.When the common control information indicates that the currentlyreceived PPDU is for a single VHT-STA (including SU-MIMO), STAs may bedesigned not to decode the VHT-SIG-B field.

The VHT-SIG-B field includes information about modulation, encoding andrate matching of each VHT-STA. The size of the VHT-SIG-B field maydepend on MIMO transmission type (MU-MIMO or SU-MIMO) and a channelbandwidth used for PPDU transmission.

In a system supporting MU-MIMO, in order to transmit PPDUs having thesame size to STAs paired with an AP, information indicating the size ofthe bits of a data field forming the PPDU and/or information indicatingthe size of bit streams forming a specific field may be included in theVHT-SIG-A field.

In this case, an L-SIG field may be used to effectively use a PPDUformat. A length field and a rate field which are included in the L-SIGfield and transmitted so that PPDUs having the same size are transmittedto all of STAs may be used to provide required information. In thiscase, additional padding may be required in the physical layer becausean MAC protocol data unit (MPDU) and/or an aggregate MAC PDU (A-MPDU)are set based on the bytes (or octets) of the MAC layer.

In FIG. 4, the data field is a payload and may include a service field,a scrambled PSDU, tail bits, and padding bits.

An STA needs to determine the format of a received PPDU because severalformats of PPDUs are mixed and used as described above.

In this case, the meaning that a PPDU (or a PPDU format) is determinedmay be various. For example, the meaning that a PPDU is determined mayinclude determining whether a received PPDU is a PPDU capable of beingdecoded (or interpreted) by an STA. Furthermore, the meaning that a PPDUis determined may include determining whether a received PPDU is a PPDUcapable of being supported by an STA. Furthermore, the meaning that aPPDU is determined may include determining that information transmittedthrough a received PPDU is which information.

This will be described in more detail below with reference to thedrawings.

FIG. 5 illustrates constellation diagrams for classifying a PPDU formatin a wireless communication system to which the present invention may beapplied.

(a) of FIG. 5 illustrates a constellation for the L-SIG field includedin the non-HT format PPDU, (b) of FIG. 5 illustrates a phase rotationfor HT-mixed format PPDU detection, and (c) of FIG. 5 illustrates aphase rotation for VHT format PPDU detection.

In order for an STA to classify a PPDU as a non-HT format PPDU, HT-GFformat PPDU, HT-mixed format PPDU, or VHT format PPDU, the phases ofconstellations of the L-SIG field and of the OFDM symbols, which aretransmitted following the L-SIG field, are used. That is, the STA mayclassify a PDDU format based on the phases of constellations of theL-SIG field of a received PPDU and/or of the OFDM symbols, which aretransmitted following the L-SIG field.

Referring to (a) of FIG. 5, the OFDM symbols of the L-SIG field use BPSK(Binary Phase Shift Keying).

To begin with, in order to classify a PPDU as an HT-GF format PPDU, theSTA, upon detecting a first SIG field from a received PPDU, determineswhether this first SIG field is an L-SIG field or not. That is, the STAattempts to perform decoding based on the constellation illustrated in(a) of FIG. 5. If the STA fails in decoding, the corresponding PPDU maybe classified as the HT-GF format PPDU.

Next, in order to distinguish the non-HT format PPDU, HT-mixed formatPPDU, and VHT format PPDU, the phases of constellations of the OFDMsymbols transmitted following the L-SIG field may be used. That is, themethod of modulation of the OFDM symbols transmitted following the L-SIGfield may vary, and the STA may classify a PPDU format based on themethod of modulation of fields coming after the L-SIG field of thereceived PPDU.

Referring to (b) of FIG. 5, in order to classify a PPDU as an HT-mixedformat PPDU, the phases of two OFDM symbols transmitted following theL-SIG field in the HT-mixed format PPDU may be used.

More specifically, both the phases of OFDM symbols #1 and #2corresponding to the HT-SIG field, which is transmitted following theL-SIG field, in the HT-mixed format PPDU are rotated counterclockwise by90 degrees. That is, the OFDM symbols #1 and #2 are modulated by QBPSK(Quadrature Binary Phase Shift Keying). The QBPSK constellation may be aconstellation which is rotated counterclockwise by 90 degrees based onthe BPSK constellation.

An STA attempts to decode the first and second OFDM symbolscorresponding to the HT-SIG field transmitted after the L-SIG field ofthe received PDU, based on the constellations illustrated in (b) of FIG.5. If the STA succeeds in decoding, the corresponding PPDU may beclassified as an HT format PPDU.

Next, in order to distinguish the non-HT format PPDU and the VHT formatPPDU, the phases of constellations of the OFDM symbols transmittedfollowing the L-SIG field may be used.

Referring to (c) of FIG. 5, in order to classify a PPDU as a VHT formatPPDU, the phases of two OFDM symbols transmitted after the L-SIG fieldmay be used in the VHT format PPDU.

More specifically, the phase of the OFDM symbol #1 corresponding to theVHT-SIG-A coming after the L-SIG field in the HT format PPDU is notrotated, but the phase of the OFDM symbol #2 is rotated counterclockwiseby 90 degrees. That is, the OFDM symbol #1 is modulated by BPSK, and theOFDM symbol #2 is modulated by QBPSK.

The STA attempts to decode the first and second OFDM symbolscorresponding to the VHT-SIG field transmitted following the L-SIG fieldof the received PDU, based on the constellations illustrated in (c) ofFIG. 5. If the STA succeeds in decoding, the corresponding PPDU may beclassified as a VHT format PPDU.

On the contrary, If the STA fails in decoding, the corresponding PPDUmay be classified as a non-HT format PPDU.

MAC Frame Format

FIG. 6 illustrates a MAC frame format in an IEEE 802.11 system to whichthe present invention may be applied.

Referring to FIG. 6, the MAC frame (i.e., an MPDU) includes an MACheader, a frame body, and a frame check sequence (FCS).

The MAC Header is defined as an area, including a frame control field, aduration/ID field, an address 1 field, an address 2 field, an address 3field, a sequence control field, an address 4 field, a QoS controlfield, and an HT control field.

The frame control field contains information on the characteristics ofthe MAC frame. A more detailed description of the frame control fieldwill be given later.

The duration/ID field may be implemented to have a different valuedepending on the type and subtype of a corresponding MAC frame.

If the type and subtype of a corresponding MAC frame is a PS-poll framefor a power save (PS) operation, the duration/ID field may be configuredto include the association identifier (AID) of an STA that hastransmitted the frame. In the remaining cases, the duration/ID field maybe configured to have a specific duration value depending on the typeand subtype of a corresponding MAC frame. Furthermore, if a frame is anMPDU included in an aggregate-MPDU (A-MPDU) format, the duration/IDfield included in an MAC header may be configured to have the samevalue.

The address 1 field to the address 4 field are used to indicate a BSSID,a source address (SA), a destination address (DA), a transmittingaddress (TA) indicating the address of a transmitting STA, and areceiving address (RA) indicating the address of a receiving STA.

An address field implemented as a TA field may be set as a bandwidthsignaling TA value. In this case, the TA field may indicate that acorresponding MAC frame includes additional information in a scramblingsequence. The bandwidth signaling TA may be represented as the MACaddress of an STA that sends a corresponding MAC frame, butindividual/group bits included in the MAC address may be set as aspecific value (e.g., “1”).

The sequence control field is configured to include a sequence numberand a fragment number. The sequence number may indicate a sequencenumber assigned to a corresponding MAC frame. The fragment number mayindicate the number of each fragment of a corresponding MAC frame.

The QoS control field includes information related to QoS. The QoScontrol field may be included if it indicates a QoS data frame in asubtype subfield.

The HT control field includes control information related to an HTand/or VHT transmission/reception scheme. The HT control field isincluded in a control wrapper frame. Furthermore, the HT control fieldis present in a QoS data frame having an order subfield value of 1 and amanagement frame.

The frame body is defined as an MAC payload. Data to be transmitted in ahigher layer is placed in the frame body. The frame body has a varyingsize. For example, a maximum size of an MPDU may be 11454 octets, and amaximum size of a PPDU may be 5.484 ms.

The FCS is defined as an MAC footer and used for the error search of anMAC frame.

The first three fields (i.e., the frame control field, the duration/IDfield, and Address 1 field) and the last field (i.e., the FCS field)form a minimum frame format and are present in all of frames. Theremaining fields may be present only in a specific frame type.

FIG. 7 illustrates an HT format of an HT control field in a wirelesscommunication system to which the present invention is applicable.

Referring to FIG. 7, the HT control field may include a VHT sub-field,an HT control middle sub-field, an AC constraint sub-field and a reversedirection grant (RDG)/more PPDU sub-field.

The VHT sub-field indicates whether the HT control field has an HTcontrol field format for VHT (VHT=1) or an HT control field format forHT (VHT=0). In FIG. 7, the HT control field for HT (i.e., VHT=0) isassumed.

The HT control middle sub-field may have a different format according toindication of the VHT sub-field. The HT control middle sub-field will bedescribed below in more detail.

The AC constraint sub-field indicates whether a mapped access category(AC) of a reverse direction (RD) data frame is limited to a single AC.

The RDG/more PPDU sub-field may be interpreted differently depending onwhether the corresponding field is transmitted by an RD initiator or anRD responder.

In the case of transmission by the RD initiator, the RDG/more PPDU fieldis set to “1” when an RDG is present and to “0” when an RDG is notpresent. In the case of transmission by the RD responder, the RDG/morePPDU field is set to “1” when a PPDU including the correspondingsub-field is the last frame transmitted by the RD responder and to “0”when another PPDU is transmitted.

The HT control middle sub-field of the HT control field for HT mayinclude a link adaptation sub-field, a calibration position sub-field, acalibration sequence sub-field, a reserved sub-field, a channel stateinformation (CSI)/steering sub-field, an HT null data packet (NDP)announcement sub-field, and a reserved sub-field.

The link adaption sub-field may include a training request (TRQ)sub-field, a modulation and coding scheme (MCS) request or antennaselection (ASEL) indication (MAI) sub-field, an MCS feedback sequenceidentifier (MFSI) sub-field and an MCS feedback and antenna selectioncommand/data (MFB/ASELC) sub-field.

The TRQ sub-field is set to “1” when a responder is requested totransmit a sounding PPDU and is set to “0” when the responder is notrequested to transmit a sounding PPDU.

When the MAI sub-field is set to 14, the MAI sub-field indicates ASELindication and the MFB/ASELC sub-field is interpreted as antennaselection command/data. If not, the MAI sub-field indicates MCS requestand the MFB/ASELC sub-field is interpreted as MCS feedback.

When the MAI sub-field indicates MCS request (MRQ), the MAI sub-field isconsidered to be composed of an MRQ (MCS request) and an MSI (MRQsequence identifier). The MRQ sub-field is set to “1” when MCS feedbackis request and set to “0” when MCS feedback is not requested. When theMRQ sub-field is “1”, the MSI sub-field includes a sequence number forspecifying MCS feedback request. When the MRQ sub-field is “0”, the MSIsub-field is set to a reserved bit.

The above-described sub-fields correspond to exemplary sub-fields thatmay be included in the HT control field and may be replaced by othersub-fields, or additional sub-fields may be included in the HT controlfield.

FIG. 8 illustrates a VHT format of the HT control field in a wirelesscommunication system to which the present invention is applicable.

Referring to FIG. 8, the HT control field may include a VHT sub-field,an HT control middle sub-field, an AC constraint sub-field and anRDG/more PPDU sub-field.

In FIG. 8, the HT control field for VHT (i.e., VHT=1) is assumed. The HTcontrol field for VHT may be referred to as a VHT control field.

The AC constraint sub-field and the RDG/more PPDU sub-field areidentical to those shown in FIG. 7 and thus description thereof isomitted.

As described above, the HT control middle sub-field may have a formatdepending on indication of the VHT sub-field.

The HT control middle sub-field of the HT control field for VHT mayinclude a reserved bit, an MCS feedback request (MRQ) sub-field, an MRQsequence identifier (MSI)/space-time block coding (STBC) sub-field, anMCS feedback sequence identifier (MFSI)/least significant bit (LSB) ofgroup ID (GID-L) sub-field, an MCS feedback (MFB) sub-field, an MSB ofgroup ID (GID-H) sub-field, a coding type sub-field, a feedbacktransmission (FB Tx) type sub-field and an unsolicited MFB sub-field.

Table 3 shows definition of each sub-field included in the HT controlmiddle sub-field of the VHT format.

TABLE 3 Sub-field Meaning Definition MRQ MCS request Set to “1” when MCSfeedback (solicited MFB) is requested and set to “0” if not. MSI MRQsequence When the unsolicited MFB sub-field is “0” and identifier theMRQ sub-field is set to “1”, the MSI sub-field includes a sequencenumber in the range of 0 to 6 for identifying a specific request. Whenthe unsolicited MFB sub-field is “1”, this includes a compressed MSIsub-field (2 bits) and an STBC indication sub-field (1 bit). MFSI/GID-LMFB sequence When the unsolicited MFB sub-field is set to“0”,identifier/LSB of the MFSI/GID-L sub-field includes an MSI Group IDreception value included in a frame related to MFB information. When theunsolicited MFB sub-field is set to “1” and MFB is estimated from an MUPPDU, the MFSI/GID-L sub-field includes 3 LSBs of a group ID of the PPDUfrom which MFB is estimated. MFB VHT N_STS, The MFB sub-field includesrecommended MFB. MCS, BW, SNR VHT-MCS = 15 and NUM_STS = 7 indicate thatfeedback feedback is not present. GID-H MSB of Group When theunsolicited MFB sub-field is set to“1” ID and MFB is estimated from aVHT MU PPDU, the GID-H sub-field includes 3 MSBs of a group ID of thePPDU from which unsolicited MFB is estimated. MFB is estimated from anSU PPDU and the GID-H sub-field is set to “1”. Coding Type Coding typeof When the unsolicited MFB sub-field is set to “1”, MFB response thecoding type sub-field includes coding type (BCC (binary convolutionalcode) being 0 and LDPC (low-density parity check) being 1) of a frame inwhich unsolicited MFB is estimated. FB Tx Type Transmission When theunsolicited MFB sub-field is set to“1” type of MFB and MFB is estimatedfrom an unbeamformed response VHT PPDU, the FB Tx type sub-field is setto “0”. When the unsolicited MFB sub-field is set to“1” and MFB isestimated from a beamformed VHT PPDU, the FB Tx type sub-field is set to“1”. Unsolicited Unsolicited When MFB is a response to MRQ, this is setto MFB MCS feedback “1”. indicator When MFB is not a response to MRQ,this is set to “0”.

In addition, the MFB sub-field may include a VHT NUM_STS (number ofspace time streams) sub-field, a VHT-MCS sub-field, a bandwidth (BW)sub-field and an SNR (signal to noise ratio) sub-field.

The NUM_STS sub-field indicates the number of recommended spatialstreams. The VHT-MCS sub-field indicates a recommended MCS. The BWsub-field indicates bandwidth information related to the recommendedMCS. The SNR sub-field indicates an average SNR in data subcarriers andspatial streams.

The information included in the aforementioned fields may conform todefinition of the IEEE 802.11 system. Further, the aforementioned fieldscorrespond to exemplary fields that can be included in a MAC frame butare not limited thereto. That is, the aforementioned fields may bereplaced by other fields or additional fields may be further included,and all fields may not be necessarily included.

Link Setup Procedure

FIG. 9 is a diagram illustrating a normal link setup procedure in awireless communication system to which the present invention isapplicable.

When an STA intends to set up a link for a network and transmit/receivedata, the STA needs to perform a scanning procedure for discovering thenetwork, an authentication procedure and an association procedure. Thelink setup procedure may also be referred to as a session setupprocedure. The scanning, authentication and association procedures ofthe link setup procedure may be commonly called an associationprocedure.

In WLAN, the scanning procedure is divided into a passive scanningprocedure and an active scanning procedure.

FIG. 9(a) illustrates a link setup procedure according to passivescanning and FIG. 9(b) illustrates a link setup procedure according toactive scanning.

As illustrated in FIG. 9(a), the passive scanning procedure is performedthrough a beacon frame that is periodically broadcast by an AP. Thebeacon frame, one of management frames in IEEE 802.11, is broadcastperiodically (e.g., at intervals of 100 msec) to indicate presence of awireless network such that non-AP STAs performing scanning can discoverthe wireless network and join therein. The beacon frame carriesinformation about the current network (e.g., information about a BSS).

To obtain network information, a non-AP STA waits for reception of thebeacon frame while manually changing channels. Upon reception of thebeacon frame, the non-AP STA stores the network information included inthe received beacon frame, moves to the next channel and performscanning on the next channel through the same method. When the non-APSTA receives the beacon frame to obtain the network information, thescanning procedure on the corresponding channel is completed.

In this way, the passive scanning procedure is finished when the non-APSTA receives the beacon frame without the need to transmit other framesand thus has an advantage of small overhead. However, scanning time ofthe non-AP STA increases compared to the beacon frame transmissioninterval.

The active scanning procedure, as illustrated in FIG. 9(b), a non-AP STAbroadcasts a probe request frame while actively changing channels inorder to search surrounding APs to request network information from allAPs which receive the probe request frame.

A responder that has received the probe request frame loads networkinformation in a probe response frame and transmits the probe responseframe including the network information to the non-AP STA after waitingfor a random time in order to prevent frame collision. Upon reception ofthe probe response frame, the STA may store network related informationincluded in the received probe response frame, move to the next channeland perform scanning through the same method. The scanning procedure iscompleted when the non-AP STA receives the probe response frame toacquire the network information.

The active scanning procedure has an advantage of fast scanning comparedto the passive scanning procedure. However, the active scanningprocedure requires an additional frame sequence, increasing networkoverhead.

Upon completion of the scanning procedure, the non-AP STA selects anetwork on the basis of standards thereof and then performs theauthentication procedure with respect to the corresponding AP.

The authentication procedure is performed through a process in which thenon-AP STA transmits an authentication request frame to the AP and aprocess in which the AP transmits an authentication response frame tothe non-AP STA in response to the authentication request frame, that is,2-way handshaking.

Authentication frames used for authentication request/responsecorrespond to management frames.

The authentication frames may include information about anauthentication algorithm number, an authentication transaction sequencenumber, status code, challenge text, a robust security network (RSN), afinite cyclic group, etc. Such information corresponds to an example ofinformation that may be included in the authentication request/responseframes and may be replaced by other information, or additionalinformation may be further included.

The non-AP STA may transmit the authentication request frame to the AP.The AP may determine whether to permit authentication of the non-AP STAon the basis of information included in the received authenticationrequest frame. The AP may provide an authentication processing result tothe non-AP STA through the authentication response frame.

The no-AP STA and the AP authenticate each other through theauthentication procedure and then establish association.

The association procedure is performed through a process in which thenon-AP STA transmits an association request frame to the AP and aprocess in which the AP transmits an association response frame to thenon-AP STA in response to the association request frame, that is, 2-wayhandshaking.

The association request frame may include information about variouscapabilities of the non-AP STA and information about a beacon listeninterval, a service set identifier (SSID), supported rates, supportedchannels, RSN, mobility domain, supported operating classes, trafficindication map (TIM) broadcast request, interworking servicecapabilities, etc.

Based on the association request frame, the AP determines whether thenon-AP STA is supportable. After determination, the AP loads, in theassociation response frame, information about whether the associationrequest is permitted, reason therefor and capabilities supportable bythe AP and transmits the association response frame to the non-AP STA.

The association response frame may include information about variouscapabilities and information about status code, association ID (AID),supported rates, an enhanced distributed channel access (EDCA) parameterset, a received channel power indicator (RCPI), a received signal tonoise indicator (RSNI), mobility domain, a timeout interval (associationcomeback time), an overlapping BSS scan parameter, TIM broadcastresponse, a quality of service (QOS) map, etc.

The aforementioned information that may be included in the associationrequest/response frames is exemplary and may be replaced by otherinformation or additional information may be further included.

When the non-AP STA has been successfully associated with the AP, normaltransmission and reception are performed. Conversely, when the non-APSTA has not been successfully associated with the AP, the non-AP STA mayre-attempt the association procedure or attempt association with anotherAP on the basis of the reason for the association failure.

Medium Access Mechanism

In IEEE 802.11, communication is basically different from that of awired channel environment because it is performed in a shared wirelessmedium.

In a wired channel environment, communication is possible based oncarrier sense multiple access/collision detection (CSMA/CD). Forexample, when a signal is once transmitted by a transmission stage, itis transmitted up to a reception stage without experiencing great signalattenuation because there is no great change in a channel environment.In this case, when a collision between two or more signals is detected,detection is possible. The reason for this is that power detected by thereception stage becomes instantly higher than power transmitted by thetransmission stage. In a radio channel environment, however, sincevarious factors (e.g., signal attenuation is great depending on thedistance or instant deep fading may be generated) affect a channel, atransmission stage is unable to accurately perform carrier sensingregarding whether a signal has been correctly transmitted by a receptionstage or a collision has been generated.

Accordingly, in a WLAN system according to IEEE 802.11, a carrier sensemultiple access with collision avoidance (CSMA/CA) mechanism has beenintroduced as the basic access mechanism of MAC. The CAMA/CA mechanismis also called a distributed coordination function (DCF) of IEEE 802.11MAC, and basically adopts a “listen before talk” access mechanism. Inaccordance with such a type of access mechanism, an AP and/or an STAperform clear channel assessment (CCA) for sensing a radio channel or amedium for a specific time interval (e.g., a DCF inter-frame space(DIFS)) prior to transmission. If, as a result of the sensing, themedium is determined to be an idle state, the AP and/or the STA startsto transmit a frame through the corresponding medium. In contrast, if,as a result of the sensing, the medium is determined to be a busy state(or an occupied status), the AP and/or the STA do not start theirtransmission, may wait for a delay time (e.g., a random backoff period)for medium access in addition to the DIFS assuming that several STAsalready wait for in order to use the corresponding medium, and may thenattempt frame transmission.

Assuming that several STAs trying to transmit frames are present byapplying the random backoff period, they will wait for different timesbecause the STAs stochastically have different backoff period values andwill attempt frame transmission. In this case, a collision can beminimized by applying the random backoff period.

Furthermore, the IEEE 802.11 MAC protocol provides a hybrid coordinationfunction (HCF). The HCF is based on a DCF and a point coordinationfunction (PCF). The PCF is a polling-based synchronous access method,and refers to a method for periodically performing polling so that allof receiving APs and/or STAs can receive a data frame. Furthermore, theHCF has enhanced distributed channel access (EDCA) and HCF controlledchannel access (HCCA). In EDCA, a provider performs an access method forproviding a data frame to multiple users on a contention basis. In HCCA,a non-contention-based channel access method using a polling mechanismis used. Furthermore, the HCF includes a medium access mechanism forimproving the quality of service (QoS) of a WLAN, and may transmit QoSdata in both a contention period (CP) and a contention-free period(CFP).

FIG. 10 is a diagram illustrating a random backoff period and a frametransmission procedure in a wireless communication system to which anembodiment of the present invention may be applied.

When a specific medium switches from an occupied (or busy) state to anidle state, several STAs may attempt to transmit data (or frames). Inthis case, as a scheme for minimizing a collision, each of the STAs mayselect a random backoff count, may wait for a slot time corresponding tothe selected random backoff count, and may attempt transmission. Therandom backoff count has a pseudo-random integer value and may bedetermined as one of uniformly distributed values in 0 to a contentionwindow (CW) range. In this case, the CW is a CW parameter value. In theCW parameter, CW_min is given as an initial value. If transmission fails(e.g., if ACK for a transmitted frame is not received), the CW_min mayhave a twice value. If the CW parameter becomes CW_max, it may maintainthe CW_max value until data transmission is successful, and the datatransmission may be attempted. If the data transmission is successful,the CW parameter is reset to a CW_min value. The CW, CW_min, and CW_maxvalues may be set to (2{circumflex over ( )}n)−1 (n=0, 1, 2, . . . ,).

When a random backoff process starts, an STA counts down a backoff slotbased on a determined backoff count value and continues to monitor amedium during the countdown. When the medium is monitored as a busystate, the STA stops the countdown and waits. When the medium becomes anidle state, the STA resumes the countdown.

In the example of FIG. 10, when a packet to be transmitted in the MAC ofan STA 3 is reached, the STA 3 may check that a medium is an idle stateby a DIFS and may immediately transmit a frame.

The remaining STAs monitor that the medium is the busy state and wait.In the meantime, data to be transmitted by each of an STA 1, an STA 2,and an STA 5 may be generated. When the medium is monitored as an idlestate, each of the STAs waits for a DIFS and counts down a backoff slotbased on each selected random backoff count value.

The example of FIG. 10 shows that the STA 2 has selected the smallestbackoff count value and the STA 1 has selected the greatest backoffcount value. That is, FIG. 7 illustrates that the remaining backoff timeof the STA 5 is shorter than the remaining backoff time of the STA 1 ata point of time at which the STA 2 finishes a backoff count and startsframe transmission.

The STA 1 and the STA 5 stop countdown and wait while the STA 2 occupiesthe medium. When the occupation of the medium by the STA 2 is finishedand the medium becomes an idle state again, each of the STA 1 and theSTA 5 waits for a DIFS and resumes the stopped backoff count. That is,each of the STA 1 and the STA 5 may start frame transmission aftercounting down the remaining backoff slot corresponding to the remainingbackoff time. The STA 5 starts frame transmission because the STA 5 hasa shorter remaining backoff time than the STA 1.

While the STA 2 occupies the medium, data to be transmitted by an STA 4may be generated. In this case, from a standpoint of the STA 4, when themedium becomes an idle state, the STA 4 waits for a DIFS and counts downa backoff slot corresponding to its selected random backoff count value.

FIG. 10 shows an example in which the remaining backoff time of the STA5 coincides with the random backoff count value of the STA 4. In thiscase, a collision may be generated between the STA 4 and the STA 5. Whena collision is generated, both the STA 4 and the STA 5 do not receiveACK, so data transmission fails. In this case, each of the STA 4 and theSTA 5 doubles its CW value, select a random backoff count value, andcounts down a backoff slot.

The STA 1 waits while the medium is the busy state due to thetransmission of the STA 4 and the STA 5. When the medium becomes an idlestate, the STA 1 may wait for a DIFS and start frame transmission afterthe remaining backoff time elapses.

The CSMA/CA mechanism includes virtual carrier sensing in addition tophysical carrier sensing in which an AP and/or an STA directly sense amedium.

Virtual carrier sensing is for supplementing a problem which may begenerated in terms of medium access, such as a hidden node problem. Forthe virtual carrier sensing, the MAC of a WLAN system uses a networkallocation vector (NAV). The NAV is a value indicated by an AP and/or anSTA which now uses a medium or has the right to use the medium in orderto notify another AP and/or STA of the remaining time until the mediumbecomes an available state. Accordingly, a value set as the NAVcorresponds to the period in which a medium is reserved to be used by anAP and/or an STA that transmit corresponding frames. An STA thatreceives an NAV value is prohibited from accessing the medium during thecorresponding period. The NAV may be set based on the value of theduration field of the MAC header of a frame, for example.

An AP and/or an STA may perform a procedure for exchanging a request tosend (RTS) frame and a clear to send (CTS) frame in order to providenotification that they will access a medium. The RTS frame and the CTSframe include information indicating a temporal section in which awireless medium required to transmit/receive an ACK frame has beenreserved to be accessed if substantial data frame transmission and anacknowledgement response (ACK) are supported. Another STA which hasreceived an RTS frame from an AP and/or an STA attempting to send aframe or which has received a CTS frame transmitted by an STA to which aframe will be transmitted may be configured to not access a mediumduring a temporal section indicated by information included in theRTS/CTS frame. This may be implemented by setting the NAV during a timeinterval.

UL Multiple User (MU) Transmission Method

A new frame format and numerology for an 802.11ax system, that is, thenext-generation WLAN system, are actively discussed in the situation inwhich vendors of various fields have lots of interests in thenext-generation Wi-Fi and a demand for high throughput and quality ofexperience (QoE) performance improvement are increased after 802.11ac.

IEEE 802.11ax is one of WLAN systems recently and newly proposed as thenext-generation WLAN systems for supporting a higher data rate andprocessing a higher user load, and is also called a so-called highefficiency WLAN (HEW).

An IEEE 802.11ax WLAN system may operate in a 2.4 GHz frequency band anda 5 GHz frequency band like the existing WLAN systems. Furthermore, theIEEE 802.11ax WLAN system may also operate in a higher 60 GHz frequencyband.

In the IEEE 802.11ax system, an FFT size four times larger than that ofthe existing IEEE 802.11 OFDM systems (e.g., IEEE 802.11a, 802.11n, and802.11ac) may be used in each bandwidth for average throughputenhancement and outdoor robust transmission for inter-symbolinterference. This is described below with reference to relateddrawings.

Hereinafter, in a description of an HE format PPDU according to anembodiment of the present invention, the descriptions of theaforementioned non-HT format PPDU, HT mixed format PPDU, HT-green fieldformat PPDU and/or VHT format PPDU may be reflected into the descriptionof the HE format PPDU although they are not described otherwise.

FIG. 11 is a diagram illustrating an HT (High Efficiency) format PPDUaccording to an embodiment of the present invention.

Referring to FIG. 11, an HE format PPDU for HEW may be composed of alegacy part (L-part) and an HE part (HE-part).

The L-part includes the L-STF field, L-LTF field and L-SIG field in thesame manner as that in previous WLAN systems. The L-STF field, L-LTFfield and L-SIG field may be referred to as a legacy preamble.

The HE-part is a newly defined part for 802.11ax standards and mayinclude an HE-SIG field, an HE preamble (HE-preamble) and data(HE-data). The HE-preamble may include an HE-STF field and an HE-LTFfield. In addition, the HE-STF field, HE-LTF field and HE-SIG field maybe commonly called the HE-preamble.

Although FIG. 11 illustrates the order of the HE-SIG field, HE-STF fieldand HE-LTF field, the order may be varied.

The L-part, HE-SIG field and HE-preamble may be commonly called aphysical (PHY) preamble.

The HE-SIG field may include information (e.g., OFDMA, UL MU MIMO,enhanced MCS, etc.) for decoding the HE-data field.

The L-part and the HE-part (particularly, HE-preamble and HE-data) mayhave different FFT (Fast Fourier Transform) sizes and may use differentCPs (cyclic prefixes). That is, different subcarrier frequency spacingsmay be defined for the L-part and the HE-part (particularly, HE-preambleand HE-data).

In an 802.11ax system, an FFT size four times (4×) larger than that of alegacy WLAN system may be used. That is, the L-part may have a 1× symbolstructure, and the HE-part (more specifically, HE-preamble and HE-data)may have a 4× symbol structure. In this case, the FFT of a 1×, 2×, or 4×size means a relative size for a legacy WLAN system (e.g., IEEE 802.11a,802.11n, and 802.11ac).

For example, if the sizes of FFTs used in the L-part are 64, 128, 256,and 512 in 20 MHz, 40 MHz, 80 MHz, and 160 MHz, respectively, the sizesof FFTs used in the HE-part may be 256, 512, 1024, and 2048 in 20 MHz,40 MHz, 80 MHz, and 160 MHz, respectively.

If an FFT size is larger than that of a legacy WLAN system as describedabove, subcarrier frequency spacing is reduced. Accordingly, the numberof subcarriers per unit frequency is increased, but the length of anOFDM symbol is increased.

That is, if a larger FFT size is used, it means that subcarrier spacingis narrowed. Likewise, it means that an inverse discrete Fouriertransform (IDFT)/discrete Fourier transform (DFT) period is increased.In this case, the IDFT/DFT period may mean a symbol length other than aguard interval (GI) in an OFDM symbol.

Accordingly, if an FFT size four times larger than that of the L-part isused in the HE-part (more specifically, the HE-preamble and the HE-datafield), the subcarrier spacing of the HE-part becomes ¼ times thesubcarrier spacing of the L-part, and the IDFT/DFT period of the HE-partis four times the IDFT/DFT period of the L-part. For example, if thesubcarrier spacing of the L-part is 312.5 kHz (=20 MHz/64, 40 MHz/128,80 MHz/256 and/or 160 MHz/512), the subcarrier spacing of the HE-partmay be 78.125 kHz (=20 MHz/256, 40 MHz/512, 80 MHz/1024 and/or 160MHz/2048). Furthermore, if the IDFT/DFT period of the L-part is 3.2 μs(=1/312.5 kHz), the IDFT/DFT period of the HE-part may be 12.8 μs(=1/78.125 kHz).

In this case, since one of 0.8 μs, 1.6 μs, and 3.2 μs may be used as aGI, the OFDM symbol length (or symbol interval) of the HE-part includingthe GI may be 13.6 μs, 14.4 μs, or 16 μs depending on the GI.

Although FIG. 11 illustrates a case in which the HE-SIG field isconfigured in a 1× symbol structure, the HE-SIG field may be configuredin a 4× symbol structure like the HE-preamble and HE-data.

Differently from the example shown in FIG. 11, HE-SIG may be dividedinto an HE-SIG A field and an HE-SIG B field. In this case, an FFT sizeper unit frequency may further increase after HE-SIG B. That is, an OFDMsymbol length may increase more than that in the L-part after HE-SIG B.

The HE format PPDU for a WLAN system to which the present invention isapplicable may be transmitted through at least one 20 MHz channel. Forexample, the HE format PPDU may be transmitted in a frequency band of 40MHz, 80 MHz or 160 MHz through a total of four 20 MHz channels. Thiswill be described in more detail below with reference to the attacheddrawings.

FIG. 12 is a diagram illustrating an HE format PPDU according to anembodiment of the present invention.

FIG. 12 illustrates a PPDU format when 80 MHz is allocated to a singleSTA (or OFMDA resource units are allocated to a plurality of STAs within80 MHz) or when different 80 MHz streams are respectively allocated to aplurality of STAs.

Referring to FIG. 12, L-STF, L-LTF and L-SIG may be transmitted throughOFDM symbols generated on the basis of 64 FFT points (or 64 subcarriers)on each 20 MHz channel.

A HE-SIG-A field may include common control information commonlyreceived by STAs which receive a PPDU. The HE-SIG-A field may betransmitted in 1 to 3 OFDM symbols. The HE-SIG-A field is duplicated foreach 20 MHz and contains the same information. Also, the HE-SIG-A fieldindicates full bandwidth information of the system.

Table 4 illustrates information contained in the HE-SIG-A field.

TABLE 4 Field Bits Description Bandwidth 2 Indicates a bandwidth inwhich a PPDU is transmitted. For example, 20 MHz, 40 MHz, 80 MHz or 160MHz Group ID 6 Indicates an STA or a group of STAs that will receive aPPDU Stream 12 Indicates the number or location of spatial streams forinformation each STA or the number or location of spatial streams for agroup of STAs UL indication 1 Indicates whether a PPDU is destined to anAP (uplink) or STA (downlink) MU 1 Indicates whether a PPDU is anSU-MIMO PPDU or an indication MU-MIMO PPDU GI indication 1 Indicateswhether a short GI or a long GI is used Allocation 12 Indicates a bandor a channel (subchannel index or information subband index) allocatedto each STA in a bandwidth in which a PPDU is transmitted Transmission12 Indicates a transmission power for each channel or each power STA

Information contained in each of the fields illustrated in Table 4 maybe as defined in the IEEE 802.11 system. Also, the above-describedfields are examples of the fields that may be included in the PPDU butnot limited to them. That is, the above-described fields may besubstituted with other fields or further include additional fields, andnot all of the fields may be necessarily included.

The HE-STF field is used to improve AGC estimation in MIMO transmission.

The HE-SIG-B field may include user-specific information that isrequired for each STA to receive its own data (i.e., a Physical LayerService Data Unit (PSDU)). The HE-SIG-B field may be transmitted in oneor two OFDM symbols. For example, the HE-SIG-B field may includeinformation about the length of a corresponding PSDU and the Modulationand Coding Scheme (MCS) of the corresponding PSDU.

The L-STF field, the L-LTF field, the L-SIG field, and the HE-SIG-Afield may be duplicately transmitted every 20 MHz channel. For example,when a PPDU is transmitted through four 20 MHz channels, the L-STFfield, the L-LTF field, L-STG field, and the HE-SIG-A field may beduplicately transmitted every 20 MHz channel.

If the FFT size is increased, a legacy STA that supports conventionalIEEE 802.11a/g/n/ac may be unable to decode a corresponding PPDU. Forcoexistence between a legacy STA and a HE STA, the L-STF, L-LTF, andL-SIG fields are transmitted through 64 FFT in a 20 MHz channel so thatthey can be received by a legacy STA. For example, the L-SIG field mayoccupy a single OFDM symbol, a single OFDM symbol time may be 4 μs, anda GI may be 0.8 μs.

An FFT size per unit frequency may be further increased from the HE-STF.For example, 256 FFT may be used in a 20 MHz channel, 512 FFT may beused in a 40 MHz channel, and 1024 FFT may be used in an 80 MHz channel.If the FFT size is increased, the number of OFDM subcarriers per unitfrequency is increased because spacing between OFDM subcarriers isreduced, but an OFDM symbol time may be increased. In order to improvesystem efficiency, the length of a GI after the HE-STF may be set equalto the length of the GI of the HE-SIG-A.

The HE-SIG-A field includes information that is required for a HE STA todecode a HE PPDU. However, the HE-SIG-A field may be transmitted through64 FFT in a 20 MHz channel so that it may be received by both a legacySTA and a HE STA. The reason for this is that a HE STA is capable ofreceiving conventional HT/VHT format PPDUs in addition to a HE formatPPDU. In this case, it is required that a legacy STA and a HE STAdistinguish a HE format PPDU from an HT/VHT format PPDU, and vice versa.

FIG. 13 is a drawing illustrating an HE format PPDU according to anembodiment of the present invention.

In FIG. 13, it is assumed that 20 MHz channels are allocated todifferent STAs (e.g., STA 1, STA 2, STA 3, and STA 4).

Referring to FIG. 13, an FFT size per unit frequency may be furtherincreased from the HE-SFT (or the HE-SIG-B). For example, from theHE-STF (or HE-SIG-B), 256 FFTs may be used in the 20 MHz channel, 512FFTs may be used in the 40 MHz channel, and 1024 FFTs may be used in the80 MHz channel.

Information transmitted in each field included in a PPDU is the same asthe example of FIG. 12, and thus, descriptions thereof will be omittedhereinafter.

The HE-SIG-B may include information specified to each STA but it may beencoded in the entire band (i.e., indicated in the HE-SIG-A field). Thatis, the HE-SIG-B field includes information regarding every STA andevery STA receives the HE-SIG-B field.

The HE-SIG-B field may provide frequency bandwidth information allocatedto each STA and/or stream information in a corresponding frequency band.For example, in FIG. 13, as for the HE-SIG-B, STA 1 may be allocated 20MHz, STA 2 may be allocated a next 20 MHz, STA 3 may be allocated a next20 MHz, and STA 4 may be allocated a next 20 MHz. Also, the STA 1 andSTA 2 may be allocated 40 MHz and STA 3 and STA 4 may be allocated anext 40 MHz. In this case, STA 1 and STA 2 may be allocated differentstreams and STA 3 and STA 4 may be allocated different streams.

Also, an HE-SIG C field may be defined and added to the example of FIG.13. Here, information regarding every STA may be transmitted in theentire band in the HE-SIG-B field, and control information specified toeach STA may be transmitted by 20 MHz through the HE-SIG-C field.

Also, unlike the examples of FIGS. 12 and 13, the HE-SIG-B field may notbe transmitted in the entire band but may be transmitted by 20 MHz, likethe HE-SIG-A field. This will be described with reference to FIG. 24.

FIG. 14 is a diagram illustrating an HE format PPDU according to anembodiment of the present invention.

In FIG. 14, it is assumed that 20 MHz channels are allocated todifferent STAs (e.g., STA 1, STA 2, STA 3, and STA 4).

Referring to FIG. 14, the HE-SIG-B field is not transmitted in theentire band but is transmitted by 20 MHz, like the HE-SIG-A field. Here,however, unlike the HE-SIG-A field, the HE-SIG-B field may be encoded by20 MHz and transmitted but may not be duplicated by 20 MHz andtransmitted.

Here, an FFT size per unit frequency may be further increased from theHE-STF (or the HE-SIG-B). For example, from the HE-STF (or HE-SIG-B),256 FFTs may be used in the 20 MHz channel, 512 FFTs may be used in the40 MHz channel, and 1024 FFTs may be used in the 80 MHz channel.

Information transmitted in each field included in the PPDU is the sameas the example of FIG. 12, and thus, descriptions thereof will beomitted.

The HE-SIG-A field is duplicated by 20 MHz and transmitted.

The HE-SIG-B field may provide frequency bandwidth information allocatedto each STA and/or stream information in a corresponding frequency band.Since the HE-SIG-B field includes information regarding each STA,information regarding each STA may be included in each HE-SIG-B field inunits of 20 MHz. Here, in the example of FIG. 14, 20 MHz is allocated toeach STA, but, in a case in which 40 MHz is allocated to an STA, theHE-SIG-B may be duplicated by 20 MHz and transmitted.

In a case where a partial bandwidth having a low level of interferencefrom an adjacent BSS is allocated to an STA in a situation in which eachBSS supports different bandwidths, the HE-SIG-B is preferably nottransmitted in the entire band as mentioned above.

In FIGS. 11 to 14, a data field, as payload, may include a servicefield, a scrambled PSDU, a tail bit, and a padding bit.

Meanwhile, the HE format PPDU illustrated in FIGS. 11 to 14 may bedistinguished through a repeated L-SIG (RL-SIG), a repeated symbol of anL-SIG field. The RL-SIG field is inserted in front of the HE SIG-Afield, and each STA may identify a format of a received PPDU using theRL-SIG field, as an HE format PPDU.

A method of transmitting, by an AP operating in a WLAN system, data to aplurality of STAs on the same time resource may be called downlinkmulti-user (DL MU) transmission. In contrast, a method of transmitting,by a plurality of STAs operating in a WLAN system, data to an AP on thesame time resource may be called uplink multi-user (UL MU) transmission.

Such DL MU transmission or UL MU transmission may be multiplexed on afrequency domain or a space domain.

If DL MU transmission or UL MU transmission is multiplexed on thefrequency domain, different frequency resources (e.g., subcarriers ortones) may be allocated to each of a plurality of STAs as DL or ULresources based on orthogonal frequency division multiplexing (OFDMA). Atransmission method through different frequency resources in such thesame time resources may be called “DL/UL OFDMA transmission.”

If DL MU transmission or UL MU transmission is multiplexed on the spacedomain, different spatial streams may be allocated to each of aplurality of STAs as DL or UL resources. A transmission method throughdifferent spatial streams on such the same time resources may be called“DL/UL MU MIMO transmission.”

FIGS. 15 to 17 illustrate resource allocation units in an OFDMAmulti-user transmission scheme according to an embodiment of the presentinvention.

When a DL/UL OFDMA transmission scheme is used, a plurality of resourceunits may be defined in units of n tones (or subcarriers) in a PPDUbandwidth. A resource unit refers to a frequency resource allocationunit for DL/UL OFDMA transmission.

One or more resource units are allocated per STA as DL/UL resource unitssuch that different resource units may be allocated to a plurality ofSTAs.

FIG. 15 illustrates a case in which the PPDU bandwidth is 20 MHz.

7 DC tones may be positioned in a center frequency region of the 20 MHzPPDU bandwidth. In addition, 6 left guard tones and 5 right guard tonesmay be respectively positioned at both sides of the 20 MHz PPDUbandwidth.

According to a resource unit configuration scheme illustrated in FIG.15(a), one resource unit may be composed of 26 tones (26-tone resourceunit). Here, 4 leftover tones may neighbor 26-tone resource units in the20 MHz PPDU bandwidth, as illustrated in FIG. 15(a). According to aresource unit configuration scheme illustrated in FIG. 15(b), oneresource unit may be composed of 52 tones (52-tone resource unit) or 26tones. Here, 4 leftover tones may neighbor 26-tone/52-tone resourceunits in the 20 MHz PPDU bandwidth, as illustrated in FIG. 15(b).According to a resource unit configuration scheme illustrated in FIG.15(c), one resource unit may be composed of 106 tones (106-tone resourceunit) or 26 tones. According to a resource unit configuration schemeillustrated in FIG. 15(d), one resource unit may be composed of 242tones (242-tone resource unit).

When a resource unit is configured as illustrated in FIG. 15(a), up to 9STAs may be supported for DL/UL OFDMA transmission in the 20 MHz band.When a resource unit is configured as illustrated in FIG. 15(b), up to 5STAs may be supported for DL/UL OFDMA transmission in the 20 MHz band.When a resource unit is configured as illustrated in FIG. 15(c), up to 3STAs may be supported for DL/UL OFDMA transmission in the 20 MHz band.When a resource unit is configured as illustrated in FIG. 15(d), 20 MHzmay be allocated to one STA.

On the basis of the number of STAs participating in DL/UL OFDMAtransmission and/or an amount of data transmitted or received by acorresponding STA, any one of the resource unit configuration schemesillustrated in FIGS. 15(a) to 15(d) may be applied or a combination ofthe resource unit configuration schemes of FIGS. 15(a) to 15(d) may beapplied.

FIG. 16 illustrates a case in which the PPDU bandwidth is 40 MHz.

5 DC tones may be positioned in a center frequency region of the 40 MHzPPDU bandwidth. In addition, 12 left guard tones and 11 right guardtones may be respectively positioned at both sides of the 40 MHz PPDUbandwidth.

According to a resource unit configuration scheme illustrated in FIG.16(a), one resource unit may be composed of 26 tones. Here, 16 leftovertones may neighbor 26-tone resource units in the 40 MHz PPDU bandwidth,as illustrated in FIG. 16(a). According to a resource unit configurationscheme illustrated in FIG. 16(b), one resource unit may be composed of52 tones or 26 tones. Here, 16 leftover tones may neighbor26-tone/52-tone resource units in the 40 MHz PPDU bandwidth, asillustrated in FIG. 16(b). According to a resource unit configurationscheme illustrated in FIG. 16(c), one resource unit may be composed of106 tones or 26 tones. Here, 8 leftover tones may neighbor26-tone/106-tone resource units in the 40 MHz PPDU bandwidth, asillustrated in FIG. 16(c). According to a resource unit configurationscheme illustrated in FIG. 16(d), one resource unit may be composed of242 tones. According to a resource unit configuration scheme illustratedin FIG. 16(e), one resource unit may be composed of 484 tones.

When a resource unit is configured as illustrated in FIG. 16(a), up to18 STAs may be supported for DL/UL OFDMA transmission in the 40 MHzband. When a resource unit is configured as illustrated in FIG. 16(b),up to 10 STAs may be supported for DL/UL OFDMA transmission in the 40MHz band. When a resource unit is configured as illustrated in FIG.16(c), up to 6 STAs may be supported for DL/UL OFDMA transmission in the40 MHz band. When a resource unit is configured as illustrated in FIG.16(d), up to 2 STAs may be supported for DL/UL OFDMA transmission in the40 MHz band. When a resource unit is configured as illustrated in FIG.16(e), the resource unit may be allocated to one STA for SU DL/ULtransmission in the 40 MHz band.

On the basis of the number of STAs participating in DL/UL OFDMAtransmission and/or an amount of data transmitted or received by acorresponding STA, any one of the resource unit configuration schemesillustrated in FIGS. 16(a) to 16(e) may be applied or a combination ofthe resource unit configuration schemes of FIGS. 16(a) to 16(e) may beapplied.

FIG. 17 illustrates a case in which the PPDU bandwidth is 80 MHz.

7 DC tones may be positioned in a center frequency region of the 80 MHzPPDU bandwidth. When the 80 MHz PPDU bandwidth is allocated to one STA(i.e., a resource unit composed of 996 tones is allocated to one STA),however, 5 DC tones may be positioned at the center frequency region. Inaddition, 12 left guard tones and 11 right guard tones may berespectively positioned at both sides of the 80 MHz PPDU bandwidth.

According to a resource unit configuration scheme illustrated in FIG.17(a), one resource unit may be composed of 26 tones. Here, 32 leftovertones may neighbor 26-tone resource units in the 80 MHz PPDU bandwidth,as illustrated in FIG. 17(a). According to a resource unit configurationscheme illustrated in FIG. 17(b), one resource unit may be composed of52 tones or 26 tones. Here, 32 leftover tones may neighbor26-tone/52-tone resource units in the 80 MHz PPDU bandwidth, asillustrated in FIG. 17(b). According to a resource unit configurationscheme illustrated in FIG. 17(c), one resource unit may be composed of106 tones or 26 tones. Here, 16 leftover tones may neighbor26-tone/106-tone resource units in the 80 MHz PPDU bandwidth, asillustrated in FIG. 17(c). According to a resource unit configurationscheme illustrated in FIG. 17(d), one resource unit may be composed of242 tones or 26 tones. According to a resource unit configuration schemeillustrated in FIG. 17(e), one resource unit may be composed of 484tones or 26 tones. According to a resource unit configuration schemeillustrated in FIG. 17(f), one resource unit may be composed of 996tones.

When a resource unit is configured as illustrated in FIG. 17(a), up to37 STAs may be supported for DL/UL OFDMA transmission in the 80 MHzband. Also, when a resource unit is configured as illustrated in FIG.17(b), up to 21 STAs may be supported for DL/UL OFDMA transmission inthe 80 MHz band. Also, when a resource unit is configured as illustratedin FIG. 17(c), up to 13 STAs may be supported for DL/UL OFDMAtransmission in the 80 MHz band. Also, when a resource unit isconfigured as illustrated in FIG. 17(d), up to 5 STAs may be supportedfor DL/UL OFDMA transmission in the 80 MHz band. Also, when a resourceunit is configured as illustrated in FIG. 17(e), up to 3 STAs may besupported for DL/UL OFDMA transmission in the 80 MHz band. Also, when aresource unit is configured as illustrated in FIG. 28(f), acorresponding resource unit may be allocated to one STA for SU DL/ULtransmission in the 80 MHz band.

On the basis of the number of STAs participating in DL/UL OFDMAtransmission and/or an amount of data transmitted or received by acorresponding STA, any one of the resource unit configuration schemesillustrated in FIGS. 17(a) to 17(f) may be applied or a combination ofthe resource unit configuration schemes of FIGS. 17(a) to 17(f) may beapplied.

In addition, although not shown, a resource unit configuration scheme ina case where a PPDU bandwidth is 160 MHz may also be proposed. In thiscase, the 160 MHz PPDU bandwidth may have a structure in which theaforementioned 80 MHz PPDU bandwidth is repeated twice.

Among the entire resource units determined according to theaforementioned resource unit configuration schemes, only some resourceunits may be used for DL/UL OFDMA transmission. For example, in a casewhere resource units are configured as illustrated in FIG. 17(a) within20 MHz, one resource unit is allocated to each of less than 9 STAs andthe other resource units may not be allocated to any STA.

In the case of DL OFDMA transmission, a data field of a PPDU ismultiplexed in a frequency domain by the resource unit allocated to eachSTA and transmitted.

Meanwhile, in the case of UL OFDMA transmission, each STA may configurea data field of a PPDU by the resource unit allocated thereto andsimultaneously transmit the PPDU to an AP. In this manner, since eachSTA simultaneously transmits the PPDU, the AP, a receiver, may recognizethat the data field of the PPDU transmitted from each STA is multiplexed(or frequency multiplexed) in the frequency domain and transmitted.

Also, in a case where both DL/UL OFDMA transmission and DL/UL MU-MIMOtransmission are supported, one resource unit may include a plurality ofstreams in a spatial domain. Also, one or more streams may be allocatedas a DL/UL spatial resource to one STA, and thus, different streams maybe allocated to a plurality of STAs.

For example, a resource unit comprised of 106 tones in FIG. 17(c)includes a plurality of streams in the spatial domain to support bothDL/UL OFDMA and DL/UL MU-MIMO.

Pilot Tone Plan

As described above, when an 802.11ax system uses an FFT size quadruple(4×) that of the legacy WLAN system, it is difficult to apply the pilotdeployment of the 802.11ac system. Therefore, the present inventionproposes an efficient pilot design scheme suitable for numerology of the802.11ax system by supplementing and extending the tone plan proposed in802.11n and 802.11ac systems. Accordingly, a pilot tone plan accordingto an embodiment of the present invention will be described in detailafter description of a pilot tone plan in legacy systems.

FIG. 18 illustrates pilot tone plans of legacy systems.

*802.11n System

In the 802.11n system, 4 pilot tones are inserted into subcarriers andrespectively positioned at indices of {−21, −7, 7, 21} in the case of 20MHz bandwidth transmission. In the case of 40 MHz bandwidthtransmission, 6 pilot tones are inserted into subcarriers andrespectively positioned at indices of {−53, −25, −11, 11, 25, 53}.

In the 802.11n system, a multi-stream pilot (MSP) scheme is used. Here,the MSP scheme refers to a scheme of using different pilot sequencesdepending on number of streams. Accordingly, pilot tone values (or pilotvalues) may be determined on the basis of the number of streams used fordata transmission in the MSP scheme. The 802.11n system supports up to 4streams.

In 20 MHz bandwidth transmission, pilot tones may be represented by apilot sequence expressed by Equation 1 and pilot values corresponding toindices of {−21, −7, 7, 21} may be determined as shown in the table ofFIG. 18(a). In FIG. 18(a), NSTS indicates the number of streams, iSTSindicates a stream index and Ψ_(i) _(STS) ^((N) ^(STS) ⁾ indicates apilot value.P _((i) _(STS,) _(n)) ^(−28,28)={0,0,0,0,0,0,0,Ψ_(i) _(STS) _(,n⊕4)^((N) ^(STS) ⁾,0,0,0,0,0,0,0,0,0,0,0,0,0,Ψ_(i) _(STS) _((n−1)⊕4) ^((N)^(STS) ⁾,0,0,0,0,0,0,0,0,0,0,0,0,0,Ψ_(i) _(STS) _((n−2)⊕4) ^((N) ^(STS)⁾,0,0,0,0,0,0,0,0,0,0,0,0,0,Ψ_(i) _(STS) _((n−3)⊕4) ^((N) ^(STS)⁾0,0,0,0,0,0,0}  [Equation 1]

For example, when data is transmitted using 2 streams, values of 4 pilottones transmitted through a first stream (iSTS=1) may be determined as(1, 1, −1, −1) and values of 4 pilot tones transmitted through a secondstream (iSTS=2) may be determined as (1, −1, −1, 1).

Further, in 40 MHz bandwidth transmission, pilot tones may berepresented by a pilot sequence expressed by Equation 2 and pilot tonevalues corresponding to indices of {−53, −25, −11, 11, 25, 53} may bedetermined as shown in the table of FIG. 18(b). In FIG. 18(b), NSTSindicates the number of streams, iSTS indicates a stream index and Ψ_(i)_(STS) ^((N) ^(STS) ⁾ indicates a pilot value.P _((i) _(STS,) _(n)) ^(58,58)={0,0,0,0,0,Ψ_(i) _(STS) _(,n⊕6) ^((N)^(STS) ⁾,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,Ψ_(i)_(STS) _((n+1)⊕6) ^((N) ^(STS) ⁾,0,0,0,0,0,0,0,0,0,0,0,0,0,Ψ_(i) _(STS)_((n+2)⊕6) ^((N) ^(STS)⁾,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,Ψ_(i) _(STS) _((n+3)⊕6)^((N) ^(STS) ⁾,0,0,0,0,0,0,0,0,0,0,0,0,0,Ψ_(i) _(STS) _((n+4)⊕6) ^((N)^(STS) ⁾,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,Ψ_(i) _(STS)_((n+5)⊕6) ^((N) ^(STS) ⁾,0,0,0,0,0}  [Equation 2]

For example, when data is transmitted using 3 streams, values of 6 pilottones transmitted through a first stream (iSTS=1) may be determined as(1, 1, −1, −1, −1, −1), values of 6 pilot tones transmitted through asecond stream (iSTS=2) may be determined as (1, 1, 1, −1, 1, 1) andvalues of 6 pilot tones transmitted through a third stream (iSTS=3) maybe determined as (1, −1, 1, −1, −1, 1).

*802.11ac System

In the 802.11ac system, 4 pilot tones may be inserted into subcarriersand respectively positioned at indices of {−21, −7, 7, 21} in the caseof 20 MHz bandwidth transmission. In the case of 40 MHz bandwidthtransmission, 6 pilot tones may be inserted into subcarriers andrespectively positioned at indices of {−53, −25, −11, 11, 25, 53}. Inthe case of 80 MHz bandwidth transmission, 8 pilot tones may be insertedinto subcarriers and respectively positioned at indices of {−103, −75,−39, −11, 11, 39, 75, 103}. In the case of 160 MHz bandwidthtransmission, 16 pilot tones may be inserted into subcarriers andrespectively positioned at indices of {−231, −203, −167, −139, −117,−89, −53, −25, 25, 53, 89, 117, 139, 167, 203, 231}.

The 802.11ac system uses a single stream pilot (SSP) scheme. Here, theSSP scheme refers to a scheme of using a fixed pilot sequence per streamirrespective of the number of streams. For example, each pilot tonevalue Ψ may be determined irrespective of the number of streams as shownin the table of FIG. 18(c).

In the case of 20 MHz bandwidth transmission, pilot values of Ψ₀ to Ψ₃may be applied. Accordingly, 4 pilot tones positioned at indices of{−21, −7, 7, 21} may sequentially have values of (1, 1, 1, 1) in thecase of 20 MHz bandwidth transmission. In the case of 40 MHz bandwidthtransmission, pilot values of Ψ₀ to Ψ₅ may be applied. Accordingly, 6pilot tones positioned at indices of {−53, −25, −11, 11, 25, 53} maysequentially have values of (1, 1, 1, −1, −1, 1) in the case of 40 MHzbandwidth transmission. In the case of 80 MHz bandwidth transmission,pilot values of Ψ₀ to Ψ₇ may be applied. Accordingly, 8 pilot tonespositioned at indices of {−103, −75, −39, −11, 11, 39, 75, 103} maysequentially have values of (1, 1, 1, −1, −1, 1, 1, 1) in the case of 80MHz bandwidth transmission.

In case of 160 MHz bandwidth transmission, pilot values in 80 MHzbandwidth transmission may be duplicated and applied. Accordingly, 16pilot tones positioned at indices of {−231, −203, −167, −139, −117, −89,−53, −25, 25, 53, 89, 117, 139, 167, 203, 231} may sequentially havevalues of (1, 1, 1, −1, −1, 1, 1, 1, 1, 1, 1, −1, −1, 1, 1, 1) in thecase of 160 MHz bandwidth transmission.

Pilot tone plans in legacy systems have been described. A new pilot toneplan applicable to new systems on the basis of the above description isproposed. Particularly, the number, positions (or indices) and values(or coefficients) of pilot tones applicable to the 802.11ax system aspilot tone plans will be described in detail. The pilot tone plans maybe divided into i) a pilot tone plan in a non-OFDMA (or MIMO) scheme andii) a pilot tone plan in an OFDMA scheme.

A. Non-OFDMA Transmission (or MIMO Transmission)

The pilot tone plan in non-OFDMA transmission may include a designscheme using a tone plan of a legacy system and a design scheme notusing a tone plan of a legacy system. Hereinafter, these two schemeswill be described per bandwidth in detail.

1.20 MHz: 256 FFT

It is assumed that 256 subcarriers (or tones) of 20 MHz sequentiallyhave indices of −128 to +127.

(1) First Embodiment—Embodiment 1 Using Pilot Tone Plan of Legacy System

The Number of Pilot Tones

In the present embodiment, the number of pilot tones is 8. When thenumber of tones that can be used in 20 MHz is 242 (when the number ofleft guard tones is 6, the number of right guard tones is 5 and thenumber of DC tones is 3), the number of data tones is 234 (=242-8) if 8pilot tones are used, and thus an interleaver of the legacy system maybe used. Accordingly, use of 8 pilots in 20 MHz may be advantageous forimplementation if there is no remarkable performance deterioration.

Pilot Tone Index (or Pilot Tone Position)

If the number of guard tones and the number of DC tones of the 802.11axsystem are identical to those of a legacy system (802.11ac system),pilot tone positions in 80 MHz bandwidth transmission of the legacy(802.11ac) system may be reused as pilot tone positions in the 802.11axsystem. In this case, accordingly, 8 pilot tones may be positioned atindices of {±11, ±39, ±75, ±103}.

HE-LTF may be transmitted with a 4×FFT size (4× HE-LTF). In addition,HE-LTF may be transmitted with a 2×FFT size in which data is loaded atintervals of 2 tones (or 1 tone for 2 tones) from among subcarriers towhich 4× HE-LTF is mapped and data is not loaded (or has a value of “0”)on the remaining tones in order to reduce symbol time. Here, HE-LTF maybe transmitted as 2 HE-LTF in which data is loaded only on even-numberedtones (or tones positioned at even indices) from among tones of 4×HE-LTF and data is not loaded on odd-numbered tones (or tones positionedat even indices). In this case, accordingly, pilot tones need to beinserted into even-numbered tones (tones having even indices) from amongsubcarriers to which 4× HE-LTF is mapped. Even indices may be obtainedby adding 1 to the aforementioned indices or subtracting 1 therefrom andthe obtained even indices may be used as indices of pilot tones. Forexample, ±12 is obtained by adding 1 to ±11 and ±10 is obtained bysubtracting 1 from ±11. Such correction into an even index may beequally applied to all embodiments in which indices are odd numbers eventhough redundant description is not given.

Pilot Tone Value (Pilot Value)

In the present embodiment, a pilot tone value may be determinedaccording to the MSP scheme. Accordingly, a pilot tone value may bedetermined depending on number of streams.

FIGS. 19 to 22 are tables showing pilot tone values depending on numberof streams according to an embodiment of the present invention.Particularly, FIG. 19 shows a case in which NSTS is 1, 2 and 3, FIG. 20shows a case in which NSTS is 4 and 5, FIG. 21 shows a case in whichNSTS is 6 and 7 and FIG. 22 shows a case in which NSTS is 8.

When NSTS is 1 (NSTS=1)

When NSTS is 1, values (FIG. 18(c)) of pilot tones of 80 MHz of the802.11ac system may be used and thus pilot values of the presentembodiment may be defined as shown in the table of FIG. 19(a). In FIG.19(a), NSTS indicates the number of streams, iSTS indicates a streamindex and ψ^(NSTS,8) _(iSTS,j) indicates a value of a pilot tone at aj-th position from among 8 pilot tones in a stream having iSTS.

Pilot values of FIG. 18(c) and FIG. 19(a) are determined by applyingmirror symmetry to pilot values when NSTS=1 and iSTS=1 in the 20 MHzbandwidth of the 802.11n system. In this manner, pilot values of the 20MHz bandwidth of the 802.11n system may be reused, as represented byEquation 3.ψ^(NSTS.8) _(iSTS,j)=ψ^(NSTS.11n) _(iSTS,j)(when j=0,1,2,3) ψ^(NSTS.8)_(iSTS,j)=ψ^(NSTS.8) _(iSTS,7-j)(when j=4,5,6,7)  [Equation 3]

Here, ψ^(NSTS,11n) _(iSTS,j) denotes a value of a pilot tone at a j-thposition from among 8 pilot tones of a stream having iSTS in the 802.11nsystem.

When a legacy scheme in which various issues such as PAPR(Peak-to-Average Power Ratio) have been verified is used for pilotdesign, pilot performance may be guaranteed without additionalverification and the burden of generating new pilot sequences may bereduced in terms of hardware implementation. When NSTS is 2 to 8, pilotvalues of the 802.11n system may be reused and the above description maybe equally applied thereto.

When NSTS is 2 (NSTS=2)

When NSTS is 2, pilot values may be determined, as shown in FIG. 19(b),by applying mirror symmetry to pilot values when NSTS=2 in the 20 MHzbandwidth of the 802.11n system.

When NSTS is 3 (NSTS=3)

When NSTS is 3, pilot values may be determined, as shown in FIG. 19(c),by applying mirror symmetry to pilot values when NSTS=3 in the 20 MHzbandwidth of the 802.11n system.

When NSTS is 4 (NSTS=4)

When NSTS is 4, pilot values may be determined, as shown in FIG. 20(a),by applying mirror symmetry to pilot values when NSTS=4 in the 20 MHzbandwidth of the 802.11n system.

When NSTS is 5 to 8 (NSTS=5 to 8)

It is difficult to reuse pilot values of the 802.11n system when NSTS is5 to 8 because the 802.11n system supports up to 4 streams. Accordingly,pilot values having orthogonality maintained per stream may be obtainedby applying the property of Hadamard matrix as well as mirror symmetryto pilot values when NSTS=4 in the 20 MHz bandwidth of the 802.11nsystem and applied to cases in which NSTS=5 to 8. The property ofHadamard matrix is that if H1 and H2 are Hadamard matrices, [H1, H2; H1,−H2] are also Hadamard matrices. Here, H1 is [1, 1, 1, −1; 1, 1, −1, 1;1, −1, 1, 1; −1, 1, 1, 1] and H2 is [−1, 1, 1, 1; 1, −1, 1, 1; 1, 1, −1,1; 1, 1, 1, −1]. Pilot values generated using the aforementionedproperties are shown in FIGS. 20(b), 21 and 22.

In addition to the above Hadamard matrix, there may be various Hadamardmatrices below and pilot values when NSTS is 5 to 8 may be generatedusing such Hadamard matrices.

[H1, H1; H1, −H1], [H2, H2; H2, −H2], [H2, H1; H2, −H1], [H1, −H2; H1,H2], [H1, −H1; H1, H1], [H2, −H2; H2, H2], [H2, −H1; H2, H1], [H1, H2;−H1, H2], [H1, H1; −H1, H1], [H2, H2; −H2, H2], [H1, H1; H1, −H1], [H2,H1; −H2, H1], [−H1, H2; H1, H2], [−H1, H1; H1, H1], [−H2, H2; H2, H2],[−H2, H1; H2, H1], [H1, H2; H1, −H2], [H1, H2; −H1, H2]

Here, use of pilot values generated using the Hadamard matrix of [H1,H2; H1, −H2] or [H1, H2; −H1, H2] corresponds to reuse of pilot tonevalues in the 80 MHz bandwidth of the 802.11ac system.

When pilot values having orthogonality maintained per stream are used,transport diversity can be enhanced and undesired beamforming effectscan be reduced.

(2) Second Embodiment—Embodiment 2 Using Pilot Tone Plan of LegacySystem

The Number/Indices of Pilot Tones

In the present embodiment, the number and indices of pilot tones conformto the scheme proposed in the first embodiment.

Pilot Tone Value (Pilot Value)

A unified SSP scheme that extends pilot values when NSTS=8 in the firstembodiment to pilot values when NSTS=1 to 7 and uses the pilot values aspilot tone values is proposed. According to this SSP scheme, pilot tonesof each stream may have fixed pilot values irrespective of the number ofstreams. For example, when pilot values shown in FIG. 22 are used, pilottones of the first stream (iSTS=1) may have a fixed pilot sequence of(1, 1, 1, −1, −1, 1, 1, 1) irrespective of the number of streams.

When unified pilot values are used in this manner, system configurationis simplified and the burden of implementation of hardware is reduced.

(3) Third Embodiment—Embodiment of Deciding Pilot Values Through PilotSequence Pairing

The Number/Indices of Pilot Tones

In the present embodiment, the number and indices of pilot tones conformto the scheme proposed in the first embodiment.

Pilot Tone Values (Pilot Values)

FIG. 23 is a table showing sequence groups for generating pilot valuesaccording to an embodiment of the present invention. In FIG. 23,orthogonality is maintained between sequences of groups A to C. Further,the sequence of group B and the sequence of group C have opposite signsat the same index.

8 sequences having a length of 8 may be generated by one-to-one mappingthe sequence of group A to the sequence of group B and one-to-onemapping the sequence of group A to the sequence of group C. Duringmapping, sequences having the same index are mapped and orthogonality ismaintained between the 8 sequences generated. The 8 sequences generatedin this manner may be applied as fixed pilot sequences of a streamhaving a specific index (iSTS) according to the SSP scheme. Here, streamindices (iSTS=1 to 8) may be randomly assigned to the 8 pilot sequences.

(4) Fourth Embodiment—Embodiment of Using Some Pilot Positions

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 4.

Index of Pilot Tone (Position of Pilot Tone)

In the present embodiment, 4 pilot tone indices are selected from pilottone indices {±11, ±39, ±75, ±103} proposed in the first to thirdembodiments and used.

As an embodiment, pilot tone indices may be selected from the indicesproposed in the first to third embodiments at intervals of two from thefirst index. In this case, pilot tone indices may be {−103, −39, +11,+75}.

As another embodiment, pilot tone indices may be selected from theindices proposed in the first to third embodiments at intervals of twofrom the second index. In this case, pilot tone indices may be {−75,−11, +39, +103}.

As another embodiment, pilot tone indices may be selected such thatnegative indices and positive indices are symmetrical in the first tothird embodiments. Accordingly, pilot tone indices may be {±11, ±39},{±11, ±75}, {±11, ±103}, {±39, ±75}, {±39, ±103} or {±75, ±103}.

Pilot Tone Value (Pilot Value)

Pilot tone values conform to a scheme proposed in the twenty-eighth,twenty-ninth or thirtieth embodiment which will be described below. Thiswill be described in detail below.

(5) Fifth Embodiment—Embodiment of Applying Pilot Tone Plan of 802.11acSystem

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 4.

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices may be obtained by 4×upscaling pilot tone indices of the 20 MHz bandwidth in the 802.11acsystem. In this case, upscaled pilot indices may be {±28, ±84}.

Pilot Tone Value (Pilot Value)

Pilot tone values conform to the scheme proposed in the twenty-eighth,twenty-ninth or thirtieth embodiment which will be described below. Thiswill be described in detail below.

(6) Sixth Embodiment—Embodiment of Deciding the Number of Pilot TonesDepending on Number of Streams

When the number of pilot tones is reduced, the number of data tones(tones carrying data) increases and thus a larger amount of data may betransmitted. However, as many orthogonal sequences as a reduced numberof pilot tones cannot be generated. Accordingly, a scheme of applyingthe number of pilot tones depending on a total number of streams isproposed in order to increase the amount of transmitted data as follows.

The scheme proposed in the fifth embodiment is employed when the totalnumber of streams is less than 4 and one of the schemes proposed in thefirst to fourth embodiments is employed when the total number of streamsis 4 to 8.

(7) Seventh Embodiment—Embodiment of Using the Same Pilot SequenceIrrespective of the Number of Streams

The present embodiment proposes a pilot tone plan that applies one fixedpilot sequence irrespective of the number of streams as in the SSPscheme of the 802.11ac system.

Accordingly, when the number of pilot tones is 8, pilot tone indices (orpositions) and values may conform to the scheme proposed in the firstembodiment when NSTS=1. When the number of pilot tones is 4, pilot toneindices (or positions) may conform to the scheme proposed in the fifthembodiment and pilot tone values may conform to the scheme proposed inthe twenty-eighth embodiment which will be described below.

This pilot tone plan is proposed because overhead for using a pluralityof orthogonal pilot sequences in a MIMO situation in which data istransmitted and received using multiple streams is large compared toperformance obtained by using the orthogonal pilot sequences.Accordingly, overhead can be reduced by introducing the SSP scheme thatapplies a fixed pilot sequence irrespective of the number of streams.

2. 40 MHz: 512 FFT

It is assumed that 512 subcarriers (or tones) of the 40 MHz bandwidthsequentially have indices of −256 to +255.

(1) Eighth Embodiment—Extended Embodiment of First to Third Embodiments

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 16. If thenumber of tones that may be used in the 40 MHz bandwidth is 484, 484tones may be divided into 2 tone groups each having 242 (the number oftones that may be used in the 20 MHz bandwidth) tones. Here, when 16tones are used as pilot tones in each tone group, 234 (=242−16) datatones may be used, and thus an interleaver of a legacy system may beused. Accordingly, use of 16 pilots in 40 MHz may be advantageous forimplementation if there is no remarkable performance deterioration.

Pilot Tone Index (or Pilot Tone Position)

In the 802.11ac system, the pilot tone plan of the 160 MHz bandwidth isdesigned by duplicating the plot tone plan of the 80 MHz bandwidth.Similarly, the present embodiment may decide pilot tone indices of the40 MHz bandwidth by duplicating pilot tone indices (pilot tone indicesproposed in the first to third embodiments) of the 20 MHz bandwidth.Accordingly, the pilot tone indices may be determined as {±25, ±53, ±89,±117, ±139, ±167, ±203, ±231} in the present embodiment.

In this way, the scheme of duplicating a tone plan of a specificbandwidth and using the duplicated tone plan can store only one toneplan with respect to a specific bandwidth, duplicate the tone plan anduse the duplicated tone plan without storing a pilot tone plan perbandwidth, simplifying system configuration.

Pilot Tone Value (Pilot Value)

Pilot tone values of the 40 MHz bandwidth may also be designed byduplicating pilot tone values of the 20 MHz bandwidth. That is, a pilotsequence in the 40 MHz bandwidth (or a sequence of 16 pilot tonesdisposed in the 40 MHz bandwidth) may be determined as a sequenceobtained by repeating a pilot sequence in the 20 MHz bandwidth (or asequence of 8 pilot tones disposed in the 20 MHz bandwidth) twice. Thismay be represented by the following equation 4.ψ^(NSTS,16) _(iSTS,j)=ψ^(NSTS,8) _(iSTS,j, mod(j,8))  [Equation 4]

Here, NSTS indicates the number of streams, iSTS indicates a streamindex, ψ^(NSTS,16) _(iSTS,j) denotes a value of a pilot tone at a j-thposition from among 16 pilot tones included in the 40 MHz bandwidth in astream having iSTS, and ψ^(NSTS,8) _(iSTS, mod(j,8)) denotes a value ofa pilot tone at a mod(j,8)-th position from among 8 pilot tones includedin the 20 MHz bandwidth in a stream having iSTS.

(9) Ninth Embodiment—Extended Embodiment of Fourth and Fifth Embodiments

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 8. In legacysystems, the number of pilot tones used in the 40 MHz bandwidth is lessthan the number of pilot tones of the 80 MHz bandwidth and greater thanthe number of pilot tones of the 20 MHz bandwidth. Based on this, it maybe desirable to use 8 or less pilot tones in the 40 MHz bandwidth if 8pilot tones are used in the 80 MHz bandwidth in order to improve peakthroughput. Further, it 8 pilot tones need to be used in the 20 MHzbandwidth in order to reuse a legacy interleaver, it may be desirable touse 8 or more pilot tones in the 40 MHz bandwidth. Accordingly, thepresent embodiment proposes use of 8 pilot tones in the 40 MHz bandwidthto satisfy the two conditions.

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices are obtained byduplicating pilot tone indices proposed in the fourth and fifthembodiments.

Pilot tone indices generated by duplicating pilot tone indices {±11,±39, ±75, ±103} proposed in the fourth and fifth embodiments are{(−103/−231,25), (−75/−203,53), (−39/−167,89), (−11/−139,117),(11/−117,139), (39/−89,167), (75/−53,203), (103/−25,231), (−84/−212,44),(−28/−156,100), (28/−100,156), (84/−44,212)}.

Here, numerals at the left of “/” indicate pilot tone indices beforeduplication, that is, pilot tone indices {±11, ±39}, {±11, ±75}, {±11,±103}, {±39, ±75}, {±39, ±103}, {±75, ±103}, {±28, ±84} proposed in thefourth and fifth embodiments, and numerals at the right of “/” indicatepilot tone indices after duplication, that is, pilot tone indicesproposed in the present embodiment. Accordingly, if pilot tone indices{±39, ±103} proposed in the fourth embodiment are duplicated and used,indices {±25, ±89, ±167, ±231} may be generated according to theaforementioned duplication scheme and pilot tones may be positioned atsuch indices.

In the fourth and fifth embodiment and the present embodiment, a pilottone index may be corrected into an even index by adding 1 thereto orsubtracting 1 therefrom for application of 2× HE-LTF, as describedabove. For example, {±39, ±103} may be corrected into {±40, ±104}(={±(39+1), ±(103+1)}). Also, {±40, ±104} may be duplicated andcorrected into {±26, ±90, ±168, ±232} (={±26, ±90, ±168, ±232}). Suchduplication and correction into an even index may be equally applied toembodiments in which indices are odd numbers even though redundantdescription is not given.

Pilot Tone Value (Pilot Value)

In the present embodiment, pilot values conform to the scheme proposedin the first, second or third embodiment.

(3) Tenth Embodiment—Extended Embodiment of First to Third Embodiments

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 8.

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices are obtained by 2×upscaling pilot tone indices proposed in the first to third embodiments.Upscaled pilot tone indices may be {±22, ±78, ±150, ±206}.

Pilot Tone Value (Pilot Value)

In the present embodiment, pilot values conform to the scheme proposedin the first, second or third embodiment.

(4) Eleventh Embodiment—Embodiment of Using Only Some Pilot Positions

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 8.

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, 8 pilot tone indices are selected from pilottone indices {±25, ±53, ±89, ±117, ±139, ±167, ±203, ±231} proposed inthe eighth embodiment and used.

As an embodiment, pilot tone indices may be selected from the proposedindices at intervals of two from the first index. In this case, pilottone indices may be {−231, −167, −117, −53, +25, +89, +139, +203}.

As another embodiment, pilot tone indices may be selected from theproposed indices at intervals of two from the first index. In this case,pilot tone indices may be {−203, −139, −89, −25, +53, +117, +167, +231}.

As another embodiment, pilot tone indices may be selected such that anegative index and a positive index are symmetrical. Accordingly, pilottone indices may be {±25, ±53, ±89, ±117}, {±25, ±53, ±89, ±139}, {±25,±53, ±89, ±167}, {±25, ±53, ±89, ±203}, {±25, ±53, ±89, ±231}, {±25,±53, ±117, ±139}, {±25, ±53, ±117, ±167}, {±25, ±53, ±117, ±203}, {±25,±53, ±117, ±231}, {±25, ±53, ±139, ±167}, {±25, ±53, ±139, ±203}, {±25,±53, ±139, ±231}, {±25, ±53, ±167, ±203}, {±25, ±53, ±167, ±231}, {±25,±53, ±203, ±231}, {±25, ±89, ±117, ±139}, {±25, ±89, ±117, ±167}, {±25,±89, ±117, ±203}, {±25, ±89, ±117, ±231}, {±25, ±89, ±139, ±167}, {±25,±89, ±139, ±203}, {±25, ±89, ±139, ±231}, {±25, ±89, ±167, ±203}, {±25,±89, ±167, ±231}, {±25, ±89, ±203, ±231}, {±25, ±117, ±139, ±167}, {±25,±117, ±139, ±203}, {±25, ±117, ±139, ±231}, {±25, ±117, ±167, ±203},{±25, ±117, ±167, ±231}, {±25, ±117, ±203, ±231}, {±25, ±139, ±167,±203}, {±25, ±139, ±167, ±231}, {±25, ±139, ±203, ±231}, {±25, ±167,±203, ±231}, {±53, ±89, ±117, ±139}, {±53, ±89, ±117, ±167}, {±53, ±89,±117, ±203}, {±53, ±89, ±117, ±231}, {±53, ±89, ±139, ±167}, {±53, ±89,±139, ±203}, {±53, ±89, ±139, ±231}, {±53, ±89, ±167, ±203}, {±53, ±89,±167, ±231}, {±53, ±89, ±203, ±231}, {±53, ±117, ±139, ±167}, {±53,±117, ±139, ±203}, {±53, ±117, ±139, ±231}, {±53, ±117, ±167, ±203},{±53, ±117, ±167, ±231}, {±53, ±117, ±203, ±231}, {±53, ±139, ±167,±203}, {±53, ±139, ±167, ±231}, {±53, ±139, ±203, ±231}, {±53, ±167,±203, ±231}, {±89, ±117, ±139, ±167}, {±89, ±117, ±139, ±203}, {±89,±117, ±139, ±231}, {±89, ±117, ±167, ±203}, {±89, ±117, ±167, ±231},{±89, ±117, ±203, ±231}, {±89, ±139, ±167, ±203}, {±89, ±139, ±167,±231}, {±89, ±167, ±203, ±231}, {±117, ±139, ±167, ±203}, {±117, ±139,±167, ±231}, {±117, ±167, ±203, ±231} or {±139, ±167, ±203, ±231}.

Pilot Tone Value (Pilot Value)

In the present embodiment, pilot values conform to the scheme proposedin the first, second or third embodiment.

(5) Twelfth Embodiment—Embodiment Having the Same Number of Pilot Tonesas that in 802.11ac System

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 6 as in the802.11 ac system.

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices are {±44, ±100, ±212}which are obtained by 4× upscaling pilot tone indices of the 40 MHzbandwidth in the 802.11 ac system according to 512 FFT size.

Pilot Tone Value (Pilot Value)

In the present embodiment, pilot values conform to a scheme proposed inthe thirty-second, thirty-third or thirty-fourth embodiment which willbe described below.

(6) Thirteenth Embodiment—Embodiment of Deciding the Number of PilotTones Depending on the Number of Streams

A scheme of applying the number of pilot tones depending on a totalnumber of streams to increase the amount of transmitted data isproposed. The scheme proposed in the twelfth embodiment is employed whenthe total number of streams is less than 6, one of the schemes proposedin the ninth to eleventh embodiments is employed when the total numberof streams is 6 to 8, and the scheme proposed in the eight embodiment isemployed when the total number of streams is 9 to 16.

(7) Fourteenth Embodiment—Embodiment of Using the Same Pilot SequenceIrrespective of the Number of Streams

The present embodiment proposes a pilot tone plan that applies one fixedpilot sequence irrespective of the number of streams as in the SSPscheme of the 802.11ac system.

Accordingly, when the number of pilot tones is 16, pilot tone indices(or positions) may conform to the scheme proposed in the eighthembodiment and pilot tone values may be obtained by duplicating pilottone values proposed when NSTS=1 in the first embodiment twice.

When the number of pilot tones is 8, pilot tone indices may conform tothe scheme proposed in the tenth embodiment and pilot tone values mayconform to the scheme proposed when NSTS=1 in the first embodiment.

Further, when the number of pilot tones is 6, pilot tone indices mayconform to the scheme proposed in the twelfth embodiment and pilot tonevalues may conform to a scheme proposed when NSTS=1 in the thirty-secondembodiment which will be described below.

This pilot tone plan is proposed because overhead for using a pluralityof orthogonal pilot sequences in a MIMO situation in which data istransmitted and received using multiple streams is large compared toperformance obtained by using the orthogonal pilot sequences.Accordingly, overhead can be reduced by introducing the SSP scheme thatapplies a fixed pilot sequence irrespective of the number of streams.

3. 80 MHz: 1024 FFT

It is assumed that 1024 subcarriers (or tones) of the 80 MHz bandwidthsequentially have indices of −512 to +511.

(1) Fifteenth Embodiment—Extended Embodiment of First, Second, Third orEighth Embodiment

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 32.

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices of the 80 MHz bandwidthmay be determined by duplicating pilot tone indices of the 20 MHzbandwidth (pilot tone indices proposed in the first to thirdembodiments) four times. Further, pilot tone indices of the 80 MHzbandwidth may be determined by duplicating pilot tone indices of the 40MHz bandwidth (pilot tone indices proposed in the eighth embodiment)twice. In this case, the determined pilot tone indices may be {±25, ±53,±89, ±117, ±139, ±167, ±203, ±231, ±281, ±309, ±345, ±373, ±395, ±423,±459, ±487}.

In this way, the scheme of duplicating a tone plan of a specificbandwidth and using the duplicated tone plan can store only one toneplan with respect to a specific bandwidth, duplicate the tone plan anduse the duplicated tone plan without storing a pilot tone plan perbandwidth, simplifying system configuration.

Pilot Tone Value (Pilot Value)

Pilot tone values of the 80 MHz bandwidth may also be designed byduplicating pilot tone values of the 20 MHz bandwidth. That is, a pilotsequence in the 80 MHz bandwidth (or a sequence of 32 pilot tonesdisposed in the 80 MHz bandwidth) may be determined as a sequenceobtained by repeating a pilot sequence in the 20 MHz bandwidth (or asequence of 8 pilot tones disposed in the 20 MHz bandwidth) four times.This may be represented by the following equation 5.ψ^(NSTS,32) _(iSTS,j)=ψ^(NSTS,8) _(iSTS, mod(j,8))  [Equation 5]

Here, NSTS indicates the number of streams, iSTS indicates a streamindex, ψ^(NSTS,32) _(iSTS,j) denotes a value of a pilot tone at a j-thposition from among 32 pilot tones included in the 80 MHz bandwidth in astream having iSTS, and ψ^(NSTS,8) _(iSTS, mod(j,8)) denotes a value ofa pilot tone at a mod(j,8)-th position from among 8 pilot tones includedin the 20 MHz bandwidth in a stream having iSTS.

In addition, pilot tone values of the 80 MHz bandwidth may be designedby duplicating pilot tone values of the 40 MHz bandwidth. That is, apilot sequence in the 80 MHz bandwidth (or a sequence of 32 pilot tonesdisposed in the 80 MHz bandwidth) may be determined as a sequenceobtained by repeating a pilot sequence in the 40 MHz bandwidth (or asequence of 16 pilot tones disposed in the 40 MHz bandwidth) twice. Thismay be represented by the following equation 6.ψ^(NSTS,32) _(iSTS,j)=ψ^(NSTS,16) _(iSTS, mod(j,16))  [Equation 6]

Here, NSTS indicates the number of streams, iSTS indicates a streamindex, ψ^(NSTS,32) _(iSTS,j) denotes a value of a pilot tone at a j-thposition from among 32 pilot tones included in the 80 MHz bandwidth in astream having iSTS, and ψ^(NSTS,8) _(iSTS, mod(j,8)) denotes a value ofa pilot tone at a mod(j, 16)-th position from among 16 pilot tonesincluded in the 40 MHz bandwidth in a stream having iSTS.

(9) Sixteenth Embodiment—Extended Embodiment of Ninth to EleventhEmbodiments

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 16. When thenumber of pilot tones included in the 80 MHz bandwidth is less than thatincluded in the 40 MHz bandwidth, performance deterioration may occur.Accordingly, it is desirable to use 16 or more pilot tones in the 80 MHzbandwidth if the number of pilot tones of the 40 MHz bandwidth is fixedto 16 and it may be desirable to use 16 pilot tones in consideration ofpeak throughput.

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices are obtained byduplicating pilot tone indices proposed in the ninth, tenth or eleventhembodiment. Duplicated pilot tone indices may be {−231/−487,25},{−203/−459,53}, {−167/−423,89}, {−139/−395,117}, {−117/−373,139},{−89/−345,167}, {−53/−309,203}, {−25/−281,231}, {25/−231,281},{53/−203,309}, {89/−167,345}, {117/−139,373}, {139/−117,395},{167/−89,423}, {203/−53,459}, {231/−25,487}, {−212/−468,44},{−156/−412,100}, {−100/−356,156}, {−44/−300,212}, {44/−212,300},{100/−156,356}, {156/−100,412}, {212/−44,468}, {−206/−462,50},{−150/−406,106}, {−78/−334,178}, {−22/−278,234}, {22/−234,278},{78/−178,334}, {150/−106,406}, or {206/−50,462}.

Here, numerals at the left of “/” indicate pilot tone indices beforeduplication, that is, pilot tone indices proposed in the ninth, tenth oreleventh embodiment, and numerals at the right of “/” indicate pilottone indices after duplication, that is, pilot tone indices proposed inthe present embodiment.

Pilot Tone Value (Pilot Value)

In the present embodiment, pilot values conform to the scheme proposedin the eighth embodiment.

(3) Seventeenth Embodiment—Embodiment of Upscaling Eighth Embodiment

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 16.

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices are obtained by 2×upscaling pilot tone indices proposed in the eighth embodiment. Upscaledpilot tone indices may be {±50, ±106, ±178, ±234, ±278, ±334, ±406,±462}.

Pilot Tone Value (Pilot Value)

In the present embodiment, pilot values conform to the scheme proposedin the eighth embodiment.

(4) Eighteenth Embodiment—Embodiment of Using Only Some Pilot Positions

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 16.

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, 16 pilot tone indices are selected from pilottone indices {±25, ±53, ±89, ±117, ±139, ±167, ±203, ±231, ±281, ±309,±345, ±373, ±395, ±423, ±459, ±487} proposed in the fifteenth embodimentand used.

As an embodiment, pilot tone indices may be selected from the proposedindices at intervals of two from the first index. In this case, pilottone indices may be {−487, −423, −373, −309, −231, −167, −117, −53, +25,+89, +139, +203, +281, +345, +395, +459}.

As another embodiment, pilot tone indices may be selected from theproposed indices at intervals of two from the first index. In this case,pilot tone indices may be {−459, −395, −345, −281, −203, −139, −89, −25,+53, +117, +167, +231, +309, +373, +423, +487}.

As another embodiment, pilot tone indices may be selected such that anegative index and a positive index are symmetrical. Accordingly, pilottone indices may be {±25, ±89, ±139, ±203, ±281, ±345, ±395, ±459}, or{±53, ±117, ±167, ±231, ±309, ±373, ±423, ±487}.

Pilot Tone Value (Pilot Value)

In the present embodiment, pilot values conform to the scheme proposedin the eighth embodiment.

(5) Nineteenth Embodiment—Embodiment Related to Equidistance andSymmetrical Pilot Tone Plan

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 16.

Pilot Tone Index

In the present embodiment, pilot tone indices have an equidistance andindices of pilot tone positions that satisfy symmetry may be {±33, ±95,±157, ±219, ±281, ±343, ±405, ±467}, {±34, ±96, ±158, ±220, ±282, ±344,±406, ±468},

{±35, ±97, ±159, ±221, ±283, ±345, ±407, ±469}.

When an equidistance and symmetry are satisfied between pilot tones asin the present embodiment, CFO (Carrier Frequency Offset) performance isimproved.

Pilot Tone Value (Pilot Value)

Pilot tone values in the present embodiment may be applied toembodiments in the specification in various manners.

(6) Twentieth Embodiment—Embodiment Having the Same Number of PilotTones as that in 802.11Ac System

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 8 as in the802.11ac system.

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices are obtained by 4×upscaling pilot tone indices of the 80 MHz bandwidth of the 802.11acsystem in consideration of 1024 FFT size. 4× upscaled pilot tone indicesmay be {±44, ±156, ±300, ±412}.

4× upscaling and use of pilot indices of a legacy system inconsideration of the 802.11ac system and the 802.11ax system may beadvantageous for system compatibility and hardware implementation.

Pilot Tone Value (Pilot Value)

In the present embodiment, pilot values conform to a scheme proposed inthe first, second or third embodiment.

(7) Twenty-First Embodiment—Embodiment of Deciding the Number of PilotTones Depending on Number of Streams

A scheme of applying the number of pilot tones depending on a totalnumber of streams to increase the amount of transmitted data isproposed. The scheme proposed in the nineteenth embodiment is employedwhen the total number of streams is less than 8, one of the schemesproposed in the sixteenth to eighteenth embodiments is employed when thetotal number of streams is 9 to 16, and the schemes proposed in thefifteenth embodiment are employed when the total number of streams is 17to 32.

(8) Twenty-Second Embodiment—Embodiment of Using the Same Pilot SequenceIrrespective of the Number of Streams

The present embodiment proposes a pilot tone plan that applies one fixedpilot sequence irrespective of the number of streams as in the SSPscheme of the 802.11ac system.

Accordingly, when the number of pilot tones is 32, pilot tone indices(or positions) may conform to the scheme proposed in the fifteenthembodiment and pilot tone values may be obtained by duplicating pilottone values (or pilot sequence) proposed when the number of pilot tonesis 16 in the fourteenth embodiment two times.

When the number of pilot tones is 16, pilot tone indices may conform tothe scheme proposed in the seventeenth embodiment and pilot tone valuesmay conform to the scheme proposed when the number of pilot tones is 16in the fourteenth embodiment.

Further, when the number of pilot tones is 8, pilot tone indices mayconform to the scheme proposed in the nineteenth embodiment and pilottone values may conform to the scheme proposed when NSTS=1 in the firstembodiment.

This pilot tone plan is proposed because overhead for using a pluralityof orthogonal pilot sequences in a MIMO situation in which data istransmitted and received using multiple streams is large compared toperformance obtained by using the orthogonal pilot sequences.Accordingly, overhead can be reduced by introducing the SSP scheme thatapplies a fixed pilot sequence irrespective of the number of streams.

4. 160 MHz: 2048 FFT

It is assumed that 1024 subcarriers (or tones) of the 80 MHz bandwidthsequentially have indices of −1024 to +1023.

(1) Twenty-Third Embodiment—Extended Embodiment of Fifteenth toEighteenth Embodiments or Twentieth Embodiment

In the present embodiment, pilot tone numbers/indexes/values proposed inthe fifteenth to eighteen embodiments or the twentieth embodiment areduplicated twice and used. Hereinafter, duplicated pilot tone indicesaccording to embodiments will be described. In the following, numeralsat the left of “/” indicate pilot tone indices before duplication andnumerals at the right of “/” indicate pilot tone indices afterduplication, that is, pilot tone indices proposed in the presentembodiment.

In the Case of the Fifteenth Embodiment (64(=2*32) Pilot Tones)

{−487:−999,25}, {−459:−971,53}, {−423:−935,89}, {−395:−907,117},{−373:−885,139}, {−345:−857,167}, {−309:−821,203}, {−281:−793,231},{−231:−743,281}, {−203:−715,309}, {−167:−679,345}, {−139:−651,373},{−117:−629,395}, {−89:−601,420}, {−53:−565,459}, {−25:−537,487},{25:−487,537}, {53:−459,565}, {89:−420,601}, {117:−395,629},{139:−373,651}, {167:−345,679}, {203:−309,715}, {231:−281,743},{281:−231,793}, {309:−203,821}, {345:−167,857}, {373:−139,885},{395:−117,907}, {423:−89,935}, {459:−53,971}, {487:−25,999}

In the Case of the Sixteenth Embodiment (32(=2*16) Pilot Tones)

{−487:−999,25}, {−459:−971,53}, {−423:−935,89}, {−395:−907,117},{−373:−885,139}, {−345:−857,167}, {−309:−821,203}, {−281:−793,231},{−231:−743,281}, {−203:−715,309}, {−167:−679,345}, {−139:−651,373},{−117:−629,395}, {−89:−601,420}, {−53:−565,459}, {−25:−537,487},{25:−487,537}, {53:−459,565}, {89:−420,601}, {117:−395,629},{139:−373,651}, {167:−345,679}, {203:−309,715}, {231:−281,743},{281:−231,793}, {309:−203,821}, {345:−167,857}, {373:−139,885},{395:−117,907}, {423:−89,935}, {459:−53,971}, {487:−25,999},{−468:−980,44}, {−412:−924,100}, {−356:−868,156}, {−300:−812,212},{−212:−724,300}, {−156:−668,356}, {−100:−612,412}, {−44:−556,468},{44:−468,556}, {100:−412,612}, {156:−356,668}, {212:−300,724},{300:−212,812}, {356:−156,868}, {412:−100,924}, {468:−44,980},{−462:−974,50}, {−406:−918,106}, {−334:−846, 178}, {−278:−790,234},{−234:−746,278}, {−178:−690,334}, {−106:−618,406}, {−50:−562,462},{50:−462,562}, {106:−406,618}, {178:−334,690}, {234:−278,746},{278:−234,790}, {334:−178,846}, {406:−106,918}, {462:−50,974}

In the Case of the Seventeenth Embodiment (32(=2*16) Pilot Tones)

{−462:−974,50}, {−406:−918,106}, {−334:−846,178}, {−278:−790,234},{−234:−746,278}, {−178:−690,334}, {−106:−618,406}, {−50:−562,462},{50:−462,562}, {106:−406,618}, {178:−334,690}, {234:−278,746},{278:−234,790}, {334:−178,846}, {406:−106,918}, {462:−50,974}

In the Case of the Eighteenth Embodiment (32(=2*16) Pilot Tones)

{−487:−999,25}, {−459:−971,53}, {−423:−935,89}, {−395:−907, 117},{−373:−885,139}, {−345:−857,167}, {−309:−821,203}, {−281:−793,231},{−231:−743,281}, {−203:−715,309}, {−167:−679,345}, {−139:−651,373},{−117:−629,395}, {−89:−601,420}, {−53:−565,459}, {−25:−537,487},{25:−487,537}, {53:−459,565}, {89:−420,601}, {117:−395,629},{139:−373,651}, {167:−345,679}, {203:−309,715}, {231:−281,743},{281:−231,793}, {309:−203,821}, {345:−167,857}, {373:−139,885},{395:−117,907}, {423:−89,935}, {459:−53,971}, {487:−25,999}

In the Case of the Twentieth Embodiment (16(=2*8) Pilot Tones)

{−412:−924,100}, {−300:−812,212}, {−156:−668,356}, {−44:−556,468},{44:−468,556}, {156:−356,668}, {300:−212,812}, {412:−100,924}

(2) Twenty-Fourth Embodiment—Embodiment of Deciding the Number of PilotTones Depending on Number of Streams

A scheme of applying the number of pilot tones depending on a totalnumber of streams to increase the amount of transmitted data isproposed. The nineteenth embodiment is duplicated and used when thetotal number of streams is less than 16, one of the sixteenth toeighteenth embodiments is duplicated and used when the total number ofstreams is 17 to 32, and the scheme proposed in the fifteenth embodimentis employed when the total number of streams is 32 to 64.

(3) Twenty-Fifth Embodiment—Embodiment of Using the Same Pilot SequenceIrrespective of Number of Streams

The present embodiment proposes a pilot tone plan that applies one fixedpilot sequence irrespective of the number of streams as in the SSPscheme of the 802.11ac system. Accordingly, pilot tonenumber/index/value proposed in the twenty-second embodiment areduplicated twice and used in the present embodiment.

This pilot tone plan is proposed because overhead for using a pluralityof orthogonal pilot sequences in a MIMO situation in which data istransmitted and received using multiple streams is large compared toperformance obtained by using the orthogonal pilot sequences.Accordingly, overhead can be reduced by introducing the SSP scheme thatapplies a fixed pilot sequence irrespective of the number of streams.

Pilot tone plans applicable to non-OFDMA transmission have beendescribed. The above-described embodiments are applicable to pilot tonesof HE-LTF and HE-data part in DL/UL and SU/MU transmission situationsand the aforementioned pilot tones may be used for tracking phases andCFO of HE-LTF and HE-data part.

B. OFDMA Transmission

In the OFDMA transmission scheme newly introduced into the 802.11axsystem, subcarriers are divided into resource units in units ofpredetermined tones, as described above with reference to FIGS. 15 to17. A detailed description will be given of a pilot tone plan perresource unit.

1.26-Tone Resource Unit

It is assumed that subcarriers (or tones) included in a 26-tone resourceunit sequentially have indices of 0 to 25. The 26-tone resource unit mayinclude 2 pilot tones. Hereinafter, indices and values of the 2 pilottones will be described in embodiments.

(1) Twenty-Sixth Embodiment

Pilot Tone Index (or Pilot Tone Position)

As an embodiment, when the 26-tone resource unit is divided into twoparts, the 2 pilot tones may be respectively positioned at the centersof the parts. In this case, accordingly, indices of the pilot tones maybe {6, 19}.

As another embodiment, the 2 pilot tones may be positioned at indiceswhich have been corrected in consideration of pilot tone spacing byexcluding DC tones and guard tones in 1 MHz 32 FFT in the 802.11ahsystem. In this case, indices of the pilot tones may be {6, 19}.

As another embodiment, the 2 pilot tones may be spaced by a distancebetween pilot tones included in 1 MHz 32 FFT in the 802.11ah system.More specifically, pilot tones are positioned at indices of −7 and +7 in1 MHz 32 FFT in the 802.11ah system, and thus the 2 pilot tones arespaced by 14. Accordingly, in consideration of such spacing andsymmetry, pilot tones of the present embodiment may be determined as {5,19} or {6, 20}.

Pilot Tone Value (Pilot Value)

FIGS. 24 and 25 are tables showing pilot tone values depending on numberof streams according to an embodiment of the present invention. In thepresent embodiment, pilot tone values may be determined according to theMSP scheme as shown in the tables of FIGS. 24 and 25. Particularly,pilot tone values may be determined as shown in the table of FIG. 24(FIG. 24(a) or FIG. 24(b)) when NSTS is 1 and pilot tone values may bedetermined as shown in the table of FIG. 25 (FIG. 25(a), FIG. 25(b) orFIG. 25(c)) when NSTS is 2. In the tables of FIGS. 24 and 25, iSTSdenotes a stream index and ψ^(NSTS,2) _(iSTS,j) denotes a value of apilot tone at a j-th position from among 2 pilot tones in a streamhaving iSTS.

In FIG. 25, i is 1 or 2, and ic is 2 when i=1 and 1 when i=2. Althoughnot shown in FIG. 25, ic may have {−1, −1} in addition to {1, 1} as asequence. While the pilot tone values shown in the tables of FIGS. 25(a)and 25(b) have orthogonality for each stream, a PAPR problem may begenerated when iSTS=ic. To solve such a PAPR problem, pilot tone valuesthat satisfy non-orthogonality per stream, as shown in FIG. 25(c), maybe proposed.

(2) Twenty-Seventh Embodiment

Pilot Tone Index

In the present embodiment, pilot tone indices conform to the schemeproposed in the twenty-sixth embodiment.

Pilot Tone Value (Pilot Value)

The present embodiment proposes a pilot tone plan that applies one fixedpilot sequence irrespective of the number of streams as in the SSPscheme of the 802.11ac system. Accordingly, pilot tone values mayconform to the scheme proposed when NSTS=1 in the twenty-sixthembodiment.

This pilot tone plan is proposed because overhead for using a pluralityof orthogonal pilot sequences in a MIMO situation in which data istransmitted and received using multiple streams is large compared toperformance obtained by using the orthogonal pilot sequences.Accordingly, overhead can be reduced by introducing the SSP scheme thatapplies a fixed pilot sequence irrespective of the number of streams.

2. 52-Tone Resource Unit

It is assumed that subcarriers (or tones) included in a 52-tone resourceunit sequentially have indices of 0 to 51. The 52-tone resource unit mayinclude 4 pilot tones. Hereinafter, indices and values of the 4 pilottones will be described in embodiments.

(1) Twenty-Eighth Embodiment

Pilot Tone Index (or Pilot Tone Position)

As an embodiment, when the 52-tone resource unit is divided into fourparts, the 4 pilot tones may be respectively positioned at the centersof the parts. In this case, accordingly, indices of the pilot tones maybe {6, 19, 32, 45}.

As another embodiment, the 4 pilot tones may be positioned at indiceswhich have been corrected in consideration of pilot tone spacing byexcluding DC tones and guard tones in the 20 MHz bandwidth of the802.11n or 802.11ac system. In this case, accordingly, indices of thepilot tones may be {5, 19, 32, 46}.

As another embodiment, the 4 pilot tones may be spaced by a distancebetween pilot tones included in the 20 MHz bandwidth of the 802.11n or802.11ac system. More specifically, since pilot tones are positioned atindices of −21, −7, +7 and +21 in the 20 MHz bandwidth of the 802.11n or802.11ac system, the 4 pilot tones are spaced by 14. Accordingly, inconsideration of such spacing and symmetry, pilot tones of the presentembodiment may be determined as {7, 21, 35, 49} or {6, 20, 34, 48}.

Pilot Tone Value (Pilot Value)

FIGS. 26 and 27 are tables showing pilot tone values depending on numberof streams according to an embodiment of the present invention. Pilotvalues of the 20 MHz bandwidth of the 802.11n system, which are shown inFIGS. 26 and 27, may be reused in the present embodiment. In FIGS. 26and 27, NSTS denotes the number of streams, iSTS denotes a stream indexand ψ^(NSTS,4) _(iSTS,j) denotes a value of a pilot tone at a j-thposition from among 4 pilot tones in a stream having iSTS.

(2) Twenty-Ninth Embodiment

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices conform to the schemeproposed in the twenty-eighth embodiment.

Pilot Tone Value (Pilot Value)

In the present embodiment, pilot tone values may be determined usingpilot values proposed when NSTS=4 in the twenty-eighth embodiment.Accordingly, pilot tones of the first stream (iSTS=1) may have a pilotsequence of {1, 1, 1, −1}, pilot tones of the second stream (iSTS=2) mayhave a pilot sequence of {1, 1, −1, 1}, pilot tones of the third stream(iSTS=3) may have a pilot sequence of {1, −1, 1, 1}, and pilot tones ofthe fourth stream (iSTS=4) may have a pilot sequence of {−1, 1, 1, 1} inthe present embodiment.

(3) Thirtieth Embodiment

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices conform to the schemeproposed in the twenty-eighth embodiment.

Pilot Tone Value (Pilot Value)

FIG. 28 is a table showing sequence groups for generating pilot valuesaccording to an embodiment of the present invention.

In the present embodiment, pilot tone values may be determined as apilot sequence generated by combining sequences of groups A and B shownin FIG. 28. For example, a pilot sequence of {1, 1, −1, −1} or {−1, −1,1, 1} may be generated using a sequence with index 1 of the group A anda sequence with index 1 of the group B. One pilot sequence generated inthis way may be equally applied to pilot tones transmitted throughstreams irrespective of the number of streams.

(4) Thirty-First Embodiment

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices conform to the schemeproposed in the twenty-eighth embodiment.

Pilot Tone Value (Pilot Value)

The present embodiment proposes a pilot tone plan that applies one fixedpilot sequence irrespective of the number of streams as in the SSPscheme of the 802.11ac system. Here, pilot tone values may conform tothe scheme proposed when NSTS=1 in the twenty-eighth embodiment.

This pilot tone plan is proposed because overhead for using a pluralityof orthogonal pilot sequences in a MIMO situation in which data istransmitted and received using multiple streams is large compared toperformance obtained by using the orthogonal pilot sequences.Accordingly, overhead can be reduced by introducing the SSP scheme thatapplies a fixed pilot sequence irrespective of the number of streams.

3. 106-Tone Resource Unit

It is assumed that subcarriers (or tones) included in a 106-toneresource unit sequentially have indices of 0 to 105.

(1) Thirty-Second Embodiment

Number of Pilot Tones

In the present embodiment, the number of pilot tones is 6.

Pilot Tone Index (or Pilot Tone Position)

As an embodiment, when the 106-tone resource unit is divided into sixparts, 6 pilot tones may be respectively positioned at the centers ofthe parts. If 2 tones can be positioned at the center of a divided partbecause the part is composed of an even number of tones, a pilot tonemay be disposed at one of the 2 tones.

As another embodiment, the 6 pilot tones may be positioned at correctedindices except DC tones and guard tones from among pilot tone indices inthe 40 MHz bandwidth of the 802.11n or 802.11ac system. In this case,indices of the pilot tones may be {1, 29, 43, 62, 76, 104}.

Pilot Tone Value (Pilot Value)

FIGS. 29 and 30 are tables showing pilot tone values depending on numberof streams according to an embodiment of the present invention. Pilotvalues of the 40 MHz bandwidth of the 802.11n system, which are shown inFIGS. 29 and 30, may be reused in the present embodiment. In FIGS. 29and 30, NSTS denotes the number of streams, iSTS denotes a stream indexand ψ^(NSTS,6) _(iSTS,j) denotes a value of a pilot tone at a j-thposition from among 6 pilot tones in a stream having iSTS.

(2) Thirty-Third Embodiment

Pilot Tone Number/Index

In the present embodiment, pilot tone number and indices conform to thescheme proposed in the thirty-second embodiment.

Pilot Tone Value (Pilot Value)

In the present embodiment, pilot tone values may be determined byextending pilot values proposed when NSTS=4 in the thirty-secondembodiment in first to fourth streams. Accordingly, pilot tones of thefirst stream (iSTS=1) may have a pilot sequence of {1, 1, −1, −1, −1,−1}, pilot tones of the second stream (iSTS=2) may have a pilot sequenceof {1, 1, 1, −1, 1, 1}, pilot tones of the third stream (iSTS=3) mayhave a pilot sequence of {1, −1, 1, −1, −1, 1} and pilot tones of thefourth stream (iSTS=4) may have a pilot sequence of {−1, 1, 1, 1, −1, 1}in the present embodiment.

(3) Thirty-Fourth Embodiment

Pilot Tone Number/Index

In the present embodiment, pilot tone number and indices conform to thescheme proposed in the thirty-second embodiment.

Pilot Tone Value (Pilot Value)

FIG. 31 is a table showing sequence groups for generating pilot valuesaccording to an embodiment of the present invention.

In the present embodiment, pilot tone values may be determined dependingon a pilot sequence generated by combining sequences of groups A, B andC. For example, a pilot sequence of {1 1 −1 −1 1 −1} may be generated bycombining a sequence with index 1 of the group A, a sequence with index2 of the group B and a sequence with index 3 of the group C. Here, asequence composed of only sequences with index 1 or 2 is excluded inconsideration of a PAPR problem. That is, {1 1 1 1 1 1} and {−1 −1 −1 −1−1 −1} are not used as pilot sequences in the present embodiment.

One pilot sequence generated in this way may be equally applied to pilottones transmitted through streams irrespective of the number of streams.

(4) Thirty-fifth Embodiment

Pilot Tone Index (or Pilot Tone Position)

In the present embodiment, pilot tone indices conform to the schemeproposed in the thirty-second embodiment.

Pilot Tone Value (Pilot Value)

The present embodiment may propose a pilot tone plan that applies onefixed pilot sequence irrespective of the number of streams as in the SSPscheme of the 802.11ac system. Here, pilot tone values may conform tothe scheme proposed when NSTS=1 in the thirty-second embodiment.

This pilot tone plan is proposed because overhead for using a pluralityof orthogonal pilot sequences in a MIMO situation in which data istransmitted and received using multiple streams is large compared toperformance obtained by using the orthogonal pilot sequences.Accordingly, overhead can be reduced by introducing the SSP scheme thatapplies a fixed pilot sequence irrespective of the number of streams.

When 4 pilot tones are used for a 106-tone resource unit, there is anadvantage that an interleaver used in the 40 MHz bandwidth of legacysystems can be reused. Hereinafter, embodiments in which a 106-toneresource unit includes 4 pilot tones will be described. Particularly,embodiments based on “indices (or positions) of pilot tones” will bedescribed below. Pilot tone indices may be determined in considerationof an equidistance and symmetry between pilot tones and pilot tonevalues conform to the scheme proposed in the twenty-eighth, twenty-ninthor thirtieth embodiment. Hereinafter, it is assumed that a 106-toneresource unit includes 4 26-tone resource units and 2 leftover tones.

(5) Thirty-sixth Embodiment

When leftover tones are positioned at both sides of a 106-tone resourceunit, indices of the 106-tone resource unit may be divided into 4 partsof i) 0 to 26 (27 tones), ii) 27 to 52 (26 tones), iii) 53 to 78 (26tones) and iv) 79 to 105 (27 tones). Here, pilot indices of {13, 39, 65,92}, {13, 40, 66, 92}, {13, 39, 66, 92} or {13, 40, 65, 92} may beproposed.

Further, when the indices are divided into 4 parts each having 26 tones(i) 1 to 26 (26 tones), ii) 27 to 52 (26 tones), iii) 52 to 78 (26tones) and iv) 79 to 104 (26 tones)) except the tones positioned at theindices 0 and 105 l on both sides of the 106-tone resource unit, pilotindices of {13, 39, 65, 91} or {14, 40, 66, 92} may be proposed.

(6) Thirty-seventh Embodiment

When leftover tones are positioned at the center of a 106-tone resourceunit, indices of the 106-tone resource unit may be divided into 4 partsof i) 0 to 25 (26 tones), ii) 26 to 52 (27 tones), iii) 53 to 79 (27tones) and iv) 80 to 105 (26 tones). Here, pilot indices of {12, 39, 66,92}, {13, 39, 66, 93}, {12, 39, 66, 93} or {12, 39, 66, 92} may beproposed.

Further, when the indices are divided into 4 parts each having 26 tones(i) 0 to 25 (26 tones), ii) 26 to 51 (26 tones), iii) 54 to 79 (26tones) and iv) 80 to 105 (26 tones)) except tones positioned at thecenter indices 52 and 53 of the 106-tone resource unit, pilot indices of{12, 38, 66, 92} or {13, 39, 67, 93} may be proposed.

(7) Thirty-eighth Embodiment

When leftover tones are positioned at the left of a 106-tone resourceunit, indices of the 106-tone resource unit may be divided into 4 partsof i) 0 to 27 (28 tones), ii) 28 to 53 (26 tones), iii) 54 to 79 (26tones) and iv) 80 to 105 (26 tones). Here, pilot indices of {13, 40, 66,92}, {14, 40, 66, 92}, {13, 41, 67, 93} or {14, 41, 67, 93} may beproposed.

Further, when the indices are divided into 4 parts each having 26 tones(i) 2 to 27 (26 tones), ii) 28 to 53 (26 tones), iii) 54 to 79 (26tones) and iv) 80 to 105 (26 tones)) except tones positioned at theindices 0 and 1 at the left of the 106-tone resource unit, pilot indicesof {14, 40, 66, 92} or {15, 41, 67, 93} may be proposed.

(8) Thirty-ninth Embodiment

When leftover tones are positioned at the right of a 106-tone resourceunit, indices of the 106-tone resource unit may be divided into 4 partsof i) 0 to 25 (26 tones), ii) 26 to 51 (26 tones), iii) 52 to 77 (26tones) and iv) 78 to 105 (28 tones). Here, pilot indices of {12, 38, 64,91}, {12, 38, 64, 92}, {13, 39, 65, 91} or {13, 39, 65, 92} may beproposed.

Further, when the indices are divided into 4 parts each having 26 tones(i) 0 to 25 (26 tones), ii) 26 to 51 (26 tones), iii) 52 to 77 (26tones) and iv) 78 to 103 (26 tones)) except tones positioned at theindices 104 and 105 at the right of the 106-tone resource unit, pilotindices of {12, 38, 64, 90} or {13, 39, 65, 91} may be proposed.

Embodiments of dividing a 106-tone resource unit into 4 parts anddeciding one of tones included in each part as a pilot tone have beendescribed in detail. Hereinafter, embodiments of using 4 pilot indicesof a 26-tone or 52-tone resource unit at a position corresponding to a106-tone resource unit as pilot tone indices of the 106-tone resourceunit will be described. Here, the 26-tone or 52-tone resource unit at aposition corresponding to a 106-tone resource unit refers to a 26-toneor 52-tone resource unit positioned at the same indices as the 106-toneresource unit within the same bandwidth. Otherwise, the 26-tone or52-tone resource unit at a position corresponding to a 106-tone resourceunit refers to a 26-tone or 52-tone resource unit included in the106-tone resource unit.

(9) Fortieth Embodiment

FIG. 32 is a diagram illustrating positions of pilot tones included in a106-tone resource unit.

When 2 leftover tones are positioned at the center of the 106-toneresource unit in order to maintain symmetry, positions of 4 pilot tones(referred to hereinafter as first to fourth pilot tones) included in the106-tone resource unit may be the same as positions of 4 pilot tonesfrom among 8 pilot tones included in 4 26-tone resource units atpositions corresponding to the 106-tone resource unit. In this case, the4 26-tone resource units and 2 leftover tones are disposed at positionscorresponding to the 106-tone resource unit, and the 2 leftover tonesmay be positioned at the center of the 4 26-tone resource units whichare sequentially arranged. More specifically, when the sequentiallyarranged 4 26-tone resource units are referred to as first to fourth26-tone resource units, the 2 leftover tones may be positioned betweenthe second and third 26-tone resource units.

Here, the position of each of the first to fourth pilot tones may be thesame as the position of one of 2 pilot tones included in each of the 426-tone resource units. For example, the position of the first pilottone may correspond to the position of one of the 2 pilot tones includedin the first 26-tone resource unit, the position of the second pilottone may correspond to the position of one of the 2 pilot tones includedin the second 26-tone resource unit, the position of the third pilottone may correspond to the position of one of the 2 pilot tones includedin the third 26-tone resource unit, and the position of the fourth pilottone may correspond to the position of one of the 2 pilot tones includedin the fourth 26-tone resource unit.

Here, the position of each of the first to fourth pilot tones may be thesame as the position of one of the 2 pilot tones included in each of the4 26-tone resource units, which is a longer distance from the leftovertones. For example, the position of the first pilot tone may correspondto the position of one of the 2 pilot tones included in the first26-tone resource unit, which is a longer distance from the leftovertones, the position of the second pilot tone may correspond to theposition of one of the 2 pilot tones included in the second 26-toneresource unit, which is a longer distance from the leftover tones, theposition of the third pilot tone may correspond to the position of oneof the 2 pilot tones included in the third 26-tone resource unit, whichis a longer distance from the leftover tones, and the position of thefourth pilot tone may correspond to the position of one of the 2 pilottones included in the fourth 26-tone resource unit, which is a longerdistance from the leftover tones. If each of the 4 26-tone resourceunits at positions corresponding to the 106-tone resource unit iscomposed of 26 tones respectively having indices of 0 to 25 and includespilot tones corresponding to indices of {6, 20}, pilot tone indexcandidates to be applied to the 106-tone resource unit may be {6, 20,32, 46, 60, 74, 86, 100}. When pilot tones at a longer distance from theleftover tones are selected from the pilot tone index candidates inconsideration of symmetry, the selected pilot tones may be {6, 32, 74,100} (refer to 32).

Further, the position of each of the first to fourth pilot tones may bethe same as the position of one of the 2 pilot tones included in each ofthe 4 26-tone resource units, which is a shorter distance from theleftover tones. For example, the position of the first pilot tone maycorrespond to the position of one of the 2 pilot tones included in thefirst 26-tone resource unit, which is a shorter distance from theleftover tones, the position of the second pilot tone may correspond tothe position of one of the 2 pilot tones included in the second 26-toneresource unit, which is a shorter distance from the leftover tones, theposition of the third pilot tone may correspond to the position of oneof the 2 pilot tones included in the third 26-tone resource unit, whichis a shorter distance from the leftover tones, and the position of thefourth pilot tone may correspond to the position of one of the 2 pilottones included in the fourth 26-tone resource unit, which is a shorterdistance from the leftover tones. If each of the 4 26-tone resourceunits at positions corresponding to the 106-tone resource unit iscomposed of 26 tones respectively having indices of 0 to 25 and includespilot tones corresponding to indices of {6, 20}, pilot tone indexcandidates to be applied to the 106-tone resource unit may be {6, 20,32, 46, 60, 74, 86, 100}. When pilot tones at a shorter distance fromthe leftover tones are selected from the pilot tone index candidates inconsideration of symmetry, the selected pilot tones may be {20, 46, 60,86}.

Further, when each of the 4 26-tone resource units at positionscorresponding to the 106-tone resource unit is composed of 26 tonesrespectively having indices of 0 to 25 and includes pilot tonescorresponding to indices of {6, 19}, pilot tone index candidates to beapplied to the 106-tone resource unit may be {6, 19, 32, 45, 60, 73, 86,99}. When 4 indices are determined from among the pilot tone indexcandidates in consideration of symmetry, the determined indices may be{6, 32, 73, 99} or {19, 45, 60, 86}.

Further, when each of the 4 26-tone resource units at positionscorresponding to the 106-tone resource unit is composed of 26 tonesrespectively having indices of 0 to 25 and includes pilot tonescorresponding to indices of {5, 19}, pilot tone index candidates to beapplied to the 106-tone resource unit may be {5, 19, 31, 45, 59, 73, 85,99}. When 4 indices are determined from among the pilot tone indexcandidates in consideration of symmetry, the determined indices may be{5, 31, 73, 99} or {19, 45, 59, 85}.

Based on the above description, the positions of the 4 pilot tones(first to fourth pilot tones) included in the 106-tone resource unit maybe the same as positions of 4 pilot tones from among 8 pilot tonesincluded in 2 52-tone resource units at positions corresponding to the106-tone resource unit. Here, the 2 52-tone resource units and 2leftover tones are disposed at positions corresponding to the 106-toneresource unit, and the 2 leftover tones may be positioned at the centerof (or between) the 2 52-tone resource units which are sequentiallyarranged.

In this case, the positions of the first to fourth pilot tones maycorrespond to positions of two of 4 pilot tones included in each of the2 52-tone resource units, as in the above case.

When pilot indices of a smaller resource unit constituting a 106-toneresource unit are used, system configuration is simplified to reducehardware burden.

(10) Forty-first Embodiment

When one leftover tone is positioned at both sides of a 106-toneresource unit in order to meet symmetry, 4 pilot tone indices of 426-tone resource units at positions corresponding to the 106-toneresource unit may be used as pilot tone indices of the presentembodiment.

If each 26-tone resource unit is composed of 26 tones respectivelyhaving indices of 0 to 25 and pilot tones are positioned at indices of{6, 19}, pilot tone index candidates to be applied to the 106-toneresource unit may be {7, 20, 33, 46, 59, 72, 85, 98}. When 4 indices aredetermined from among the pilot tone index candidates in considerationof symmetry, the determined indices may be {7, 33, 72, 98} or {20, 46,59, 85}.

Further, when each 26-tone resource unit is composed of 26 tonesrespectively having indices of 0 to 25 and pilot tones are positioned atindices of {5, 19}, pilot tone index candidates to be applied to the106-tone resource unit may be {6, 20, 32, 46, 58, 72, 84, 98}. When 4indices are determined from among the pilot tone index candidates inconsideration of symmetry, the determined indices may be {6, 32, 72, 98}or {20, 46, 58, 84}.

Further, when each 26-tone resource unit is composed of 26 tonesrespectively having indices of 0 to 25 and pilot tones are positioned atindices of {6, 20}, pilot tone index candidates to be applied to the106-tone resource unit may be {7, 21, 33, 47, 59, 73, 85, 99}. When 4indices are determined from among the pilot tone index candidates inconsideration of symmetry, the determined indices may be {7, 33, 73, 99}or {21, 47, 59, 85}.

It may be possible to decide 4 indices from among the pilot tone indexcandidates without considering symmetry. When pilot tones included in 252-tone resource units at positions corresponding to the 106-toneresource unit are used, 4 pilot tone indices of the 52-tone resourceunits may be used as pilot tone indices of the 106-tone resource unitsimilarly to the above-described case. System configuration issimplified by selectively using pilot tones of a resource unit in unitsof a smaller tone as in the above-described embodiments.

(11) Forty-second Embodiment

The present embodiment proposes use of a leftover tone as a pilot tone.

When leftover tones are positioned at the left end (e.g., indices of {0,1}) of a 106-tone resource unit, pilot tone indices of the 106-toneresource unit may be {0, 1, 104, 105} in consideration of symmetry. Thismay be equally applied when leftover tones are positioned at the rightend (e.g., indices of {104, 105}).

When only some of the leftover tones are used as pilot tones andsymmetry and equidistance of pilot tones are considered, pilot toneindices of the 106-tone resource unit may be determined as {0, 26, 79,105}, {0, 27, 78, 105} or {1, 27, 78, 104}.

When leftover tones are positioned at the center (e.g., indices of {52,53}) of the 106-tone resource unit, pilot tone indices of the 106-toneresource unit may be determined as {26, 52, 53, 79} in consideration ofsymmetry and equidistance.

4. 242-Tone Resource Unit

It is assumed that subcarriers (or tones) included in a 242-toneresource unit sequentially have indices of 0 to 241. The number andvalues of pilot tones included in the 242-tone resource unit conform tothe scheme proposed in the first to seventh embodiments. A descriptionwill be given on the basis of pilot tone indices included in the242-tone resource unit.

(1) Forty-third Embodiment

In the present embodiment, when the 242-tone resource unit is divided bythe number of pilot tones, pilot tones may be positioned at the centersof divided parts. For example, when the 242-tone resource unit includes8 pilot tones, the 242-tone resource unit may be divided into 8 partsand the 8 pilot tones may be positioned at the centers of the parts. If2 tones are positioned at the center of each part because each part iscomposed of an even number of tones, a pilot tone may correspond to oneof the 2 tones.

For example, indices of the 242-tone resource unit may be divided into 8parts of i) 0 to 30 (31 tones), ii) 31 to 60 (30 tones), iii) 61 to 90(30 tones), iv) 91 to 120 (30 tones), v) 121 to 150 (30 tones), vi) 151to 180 (30 tones), vii) 181 to 210 (30 tones), and viii) 211 to 241 (31tones). In this case, pilot ton indices may be {15, 45, 75, 105, 136,166, 196, 226}.

If the 242-tone resource unit is divided into 8 parts each of whichincludes 30 tones, except tones positioned at both sides thereof(indices of {0, 241}) (indices being i) 1 to 30 (30 tones), ii) 31 to 60(30 tones), iii) 61 to 90 (30 tones), iv) 91 to 120 (30 tones), v) 121to 150 (30 tones), vi) 151 to 180 (30 tones), vii) 181 to 210 (30tones), viii) 211 to 240 (30 tones)), pilot tone indices may be {15, 45,75, 105, 135, 165, 195, 225} or {16, 46, 76, 106, 136, 166, 196, 226}.

Further, indices of the 242-tone resource unit may be divided into 8parts of i) 0 to 29 (30 tones), ii) 30 to 59 (30 tones), iii) 60 to 89(30 tones), iv) 90 to 120 (31 tones), v) 121 to 151 (31 tones), vi) 152to 181 (30 tones), vii) 182 to 211 (30 tones), viii) 212 to 241 (30tones)). In this case, pilot tone indices may be {15, 45, 75, 105, 136,166, 196, 226}.

Here, when 2 tones positioned at the center (indices of {120, 121}) areexcluded, pilot tone indices may be {14, 44, 74, 104, 136, 166, 196,226} or {15, 45, 75, 105, 137, 167, 197, 227}.

(2) Forty-fourth Embodiment

In the present invention, pilot tones may be positioned at indices whichhave been corrected in consideration of pilot tone index spacing byexcluding DC tones and guard tones from the pilot tone indices proposedin the first to seventh embodiments. For example, when the 242-toneresource unit includes 8 pilot tones, corrected pilot tone indices maybe {19, 47, 83, 111, 130, 158, 194, 222}.

Further, in the present invention, pilot tones may be positioned atindices which have been corrected in consideration of pilot tone indexspacing by excluding only guard tones from the pilot tone indicesproposed in the first to seventh embodiments (or including only DCtones). When 8 pilot tones are present in legacy systems, the 8 pilottones are positioned at {±11, ±39, ±75, ±103}, and thus pilot toneindices of {17, 45, 81, 109, 131, 159, 195, 223} or {18, 46, 82, 110,132, 160, 196, 224} are derived in consideration of symmetry.

5. 484-tone Resource Unit

It is assumed that subcarriers (or tones) included in a 484-toneresource unit sequentially have indices of 0 to 483. The number andvalues of pilot tones included in the 484-tone resource unit conform tothe scheme proposed in the eighth to fourteenth embodiments. Adescription will be given on the basis of pilot tone indices included inthe 484-tone resource unit.

(1) Forty-fifth Embodiment

In the present embodiment, when the 484-tone resource unit is divided bythe number of pilot tones, pilot tones may be positioned at the centersof divided parts. For example, when the 484-tone resource unit includes16 pilot tones, the 484-tone resource unit may be divided into 16 partsand the 16 pilot tones may be positioned at the centers of the parts. If2 tones are positioned at the center of each part because each part iscomposed of an even number of tones, a pilot tone may correspond to oneof the 2 tones.

(2) Forty-sixth Embodiment

In the present invention, pilot tones may be positioned at indices whichhave been corrected in consideration of pilot tone index spacing byexcluding DC tones and guard tones from the pilot tone indices proposedin the eighth to fourteenth embodiments. For example, when the 484-toneresource unit includes 8 pilot tones, corrected pilot tone indices maybe {38, 94, 166, 222, 261, 317, 389, 445}.

Further, in the present invention, pilot tones may be positioned atindices which have been corrected in consideration of pilot tone indexspacing by excluding only guard tones from the pilot tone indicesproposed in the eighth to fourteenth embodiments (or including only DCtones). When 8 pilot tones are present in legacy systems, the 8 pilottones are positioned at {±22, ±78, ±150, ±206}, and thus pilot toneindices of {35, 91, 163, 219, 263, 319, 391, 447} or {36, 92, 164, 220,264, 320, 392, 448} are derived in consideration of symmetry.

(3) Forty-seventh Embodiment

In the present embodiment, the number of pilot tones is 16. Here,indices ({±25, ±53, ±89, ±117, ±139, ±167, ±203, ±231}) of the eighthembodiment are corrected to be adapted to 484 tones and used as pilottone indices of the present embodiment. The corrected indices may be{13, 41, 77, 105, 127, 155, 191, 219, 264, 292, 328, 356, 378, 406, 442,470}.

Pilot tones of the present embodiment may be positioned at indices whichhave been corrected in consideration of symmetry after excluding guardtones from the pilot tone indices proposed in the eighth embodiment(including DC tones). Corrected indices may be {10, 38, 74, 102, 124,152, 188, 216, 266, 294, 330, 358, 380, 408, 444, 472} or {11, 39, 75,103, 125, 153, 189, 217, 267, 295, 331, 359, 381, 409, 445, 473}.

Further, pilot tones of the present embodiment may be positioned atindices which have been corrected in consideration of symmetry afterexcluding 2 tones of both sides, i.e. a total of 4 tones, and dividingthe remaining indices by 30 tones (2 to 31, 32 to 61, 62 to 91, 92 to121, . . . , 452 to 481) in the pilot tone indices proposed in theeighth embodiment. In this case, pilot tone indices of {16, 46, 76, 106,136, 166, 196, 226, 256, 286, 316, 346, 376, 406, 436, 466} or {17, 47,77, 107, 137, 167, 197, 227, 257, 287, 317, 347, 377, 407, 437, 467} maybe derived.

Further, pilot tones of the present embodiment may be positioned atindices which have been corrected by excluding 4 central tones anddividing the remaining indices by 30 tones in the pilot tone indicesproposed in the eighth embodiment. In this case, pilot tone indices of{14, 44, 74, 104, 134, 164, 194, 224, 258, 288, 318, 348, 378, 408, 438,468} or {15, 45, 75, 105, 135, 165, 195, 225, 259, 289, 319, 349, 379,409, 439, 469} may be derived.

6. 996-tone Resource Unit

It is assumed that subcarriers (or tones) included in a 996-toneresource unit sequentially have indices of 0 to 995. The number andvalues of pilot tones included in the 996-tone resource unit conform tothe scheme proposed in the fifteenth to twenty-second embodiments. Adescription will be given on the basis of pilot tone indices included inthe 996-tone resource unit.

(1) Forty-eighth Embodiment

In the present embodiment, when the 996-tone resource unit is divided bythe number of pilot tones, pilot tones may be positioned at the centersof divided parts. For example, when the 996-tone resource unit includes16 pilot tones, the 484-tone resource unit may be divided into 16 partsand the 16 pilot tones may be positioned at the centers of the parts. If2 tones are positioned at the center of each part because each part iscomposed of an even number of tones, a pilot tone may correspond to oneof the 2 tones.

(2) Forty-ninth Embodiment

In the present invention, pilot tones may be positioned at indices whichhave been corrected in consideration of pilot tone index spacing byexcluding DC tones and guard tones from the pilot tone indices proposedin the fifteenth to twenty-second embodiments.

(3) Fifties Embodiment

Indices ({±50, ±106, ±178, ±234, ±278, ±334, ±406, ±462}) proposed inthe seventeenth embodiment are corrected and used as indices of pilottones of the present embodiments. The corrected indices may be {38, 94,166, 222, 266, 322, 394, 450, 545, 601, 673, 729, 773, 829, 901, 957}.

Further, pilot tones of the present embodiment may be positioned atindices which have been corrected in consideration of pilot tone indexspacing and symmetry after excluding only guard tones from the pilottone indices proposed in the seventeenth embodiment (or including onlyDC tones). Corrected indices may be {35, 91, 163, 219, 263, 319, 391,447, 547, 603, 675, 731, 775, 831, 903, 959} or {36, 92, 164, 220, 264,320, 392, 448, 548, 604, 676, 732, 776, 832, 904, 960}.

Further, pilot tones of the present embodiment may be positioned atindices which have been corrected in consideration of symmetry afterexcluding 2 tones of both sides, a total of 4 tones, and dividing theremaining indices by 62 tones (2 to 63, 64 to 125, 126 to 187, 188 to249, . . . , 932 to 993) in the pilot tone indices proposed in theseventeenth embodiment. In this case, pilot tone indices of {32, 94,156, 218, 280, 342, 404, 466, 528, 590, 652, 714, 776, 838, 900, 962} or{33, 95, 157, 219, 281, 343, 405, 467, 529, 591, 653, 715, 777, 839,901, 963} may be derived.

Further, pilot tones of the present embodiment may be positioned atindices which have been corrected by excluding central 4 tones anddividing the remaining indices by 62 tones (0 to 61, 62 to 123, . . . ,434 to 495, 500 to 561, . . . , 934 to 995) in the pilot tone indicesproposed in the seventeenth embodiment. In this case, pilot tone indicesof {30, 92, 154, 216, 278, 340, 402, 464, 530, 592, 654, 716, 778, 840,902, 964} or {31, 93, 155, 217, 279, 341, 403, 465, 531, 593, 655, 717,779, 841, 903, 965} may be derived.

Pilot tone plans proposed in non-OFDMA transmission schemes and OFDMAtransmission schemes have been described. Hereinafter, a scheme ofallocating different pilot tones to respective users in non-OFDMAtransmission will be described.

C. Method of Allocating Pilot Tone Per STA

The 802.11ax system supports UL MU transmission. In this case, an APreceives mixed signals because multiple STAs (or users) simultaneouslytransmit signals. Here, although each STA compensates for a CFO prior totransmission of a signal to the AP and then transmits the signal, theCFO is not completely compensated for due to communication failure suchas noise and a residual CFO remains. Accordingly, the AP may compensatefor the residual CFO in order to achieve reliable performance. However,since STAs have different residual CFO values, the AP requires a newscheme for allocating a pilot tone per STA, different from theabove-described schemes, to measure and compensate for a residual CFOusing a pilot tone.

In the following embodiments, pilot tone plans proposed in non-OFDMA andOFDMA schemes may be basically applied. However, different pilot tonesmay be allocated to respective STAs, and each STA may set values ofpilot tones other than a pilot tone allocated thereto to “0”. FIG. 33 isa table showing pilot tone values allocated per STA according to anembodiment of the present invention.

1. Random Allocation

The number of pilot tones may be randomly allocated to each STA.

For example, a situation in which STA 1 and STA 2 perform UL MUtransmission using one stream and a 20 MHz bandwidth is allocatedthereto may be assumed. Here, the number and indices of pilot tones mayconform to the scheme proposed in the first embodiment. In this case,second and fifth pilot tones may be randomly allocated to STA 1 and theremaining pilot tones may be allocated to STA 2. Here, pilot tone valuesmay be determined as shown in FIG. 33(a). In FIG. 33(a), iSTS denotes astream index and ψ^(NSTB,8) _(iSTS,j) denotes a value of a pilot tonedisposed at a j-th position from among 8 pilot tones in a stream havingiSTS.

In the above embodiment, different numbers of pilot tones are allocatedto the STAs and thus there may be a CFO tracking performance differencetherebetween.

2. Even Allocation

The same number of pilot tones may be allocated to STAs.

When the same number of pilot tones is allocated to STAs, pilot tonesmay remain. For example, 8 pilot tones are allocated to STAs 1, 2 and 3by 2, 2 pilot tones (=8−2*3) may remain. Here, the remaining pilot tonesmay be randomly allocated to the STAs. Otherwise, all remaining pilottones may be allocated to an STA having the highest or lowest SINR(Signal to Interference plus Noise Ratio). Otherwise, the remainingpilot tones may be allocated one by one to STAs from the STA having thehighest SINR in descending order or from the STA having the lowest SINRin ascending order. When the remaining pilot tones are allocated to anSTA having a high SINR, higher performance is guaranteed for an STAshowing higher performance, improving average throughput. When theremaining pilot tones are allocated to an STA having a low SINR,performance of an STA having low performance is enhanced to satisfy QoS.

Indices (or positions) of pilot tones allocated to each STA may be setin various manners.

As an embodiment, the AP may sequentially allocate pilot tones to STAsfrom the leftmost or rightmost pilot tone. For example, it is assumedthat 8 pilot tones are allocated to STAs 1 to 3. In this case, theleftmost first pilot tone may be allocated to STA 1, the second pilottone disposed to the right of the first pilot tone may be allocated toSTA 2, the third pilot tone disposed to the right of the second pilottone may be allocated to STA 3, and the fourth pilot tone disposed tothe right of the third pilot tone may be allocated to STA 1.Consequently, the first, fourth and seventh pilot tones are allocated toSTA 1, the second, fifth and eighth pilot tones are allocated to STA 2and the third and sixth pilot tones are allocated to STA 3.

As another embodiment, the AP may sequentially allocate pilot tones toSTAs from the leftmost or rightmost pilot tones by the number of pilottones allocated per STA.

For example, it is assumed that 3 pilot tones are allocated to STA 1, 3pilot tones are allocated to STA 2 and 2 pilot tones are allocated toSTA 3. In this case, the 8 pilot tones may be allocated from theleftmost (or rightmost) pilot tones in such a manner that 3, 3, and 2pilot tones are sequentially respectively allocated to STAs 1 to 2.Consequently, first to third pilot tones are allocated to STA 1, thefourth to sixth pilot tones are allocated to STA2 and the seventh andeighth pilot tones are allocated to STA 3. Here, the first pilot tonemay refer to the leftmost or rightmost pilot tone from among pilot tonesin the frequency band.

As another embodiment, a situation will be described in which STA 1 andSTA 2 perform UL MU transmission using one stream and a 20 MHz bandwidthis allocated thereto. Here, the number, indices and values of pilottones applied to the 20 MHz bandwidth may conform to the scheme proposedin the first embodiment. In this case, the first to fourth pilot tonesfrom among the pilot tones of the 20 MHz bandwidth may be allocated toSTA 1 and the fifth to eighth pilot tones may be allocated to STA 2according to the above description. Here, values of the pilot tonesallocated to each STA may be determined as shown in FIG. 33(b). In FIG.33(b), iSTS indicates a stream index and ψ^(NSTB,8) _(iSTS,j) indicatesa value of a pilot tone at a j-th position from among 8 pilot tones in astream having iSTS.

3. Differential Allocation

All pilot tones may be allocated to an STA having the highest or lowestSINR. Otherwise, numbers of pilot tones in proportion or inverseproportion to SINRs of STAs may be allocated to the STAs. Here, when thenumber of pilot tones calculated in proportion or inverse proportion toan SINR is not a natural number, the calculated number of pilot tonesmay be rounded off. For example, if the number of pilot tones that maybe allocated to STAs is 8 and 1.6 pilot tones and 6.4 pilot tones areallocated to STA 1 and STA 2 depending on an SINR ratio thereof, 1.6 and6.4 may be rounded off and thus 2 and 6 pilot tones may be respectivelyallocated to STA 1 and STA 2. If 2 pilot tones are allocated to STA 1and 7 pilot tones are allocated to STA 2 since the numbers of pilottones allocated to STA 1 and STA 2 are determined to be 1.5 and 6.5depending on an SINR ratio, 1 is subtracted from the larger number ofpilot tones. That is, 2 pilot tones are allocated to STA 1 and 6 pilottones are allocated to STA 2.

When pilot tones in proportion to SINR are allocated, a larger number ofpilot tones is allocated to an STA having higher performance toguarantee higher performance, improving average throughput. When pilottones in inverse proportion to an SINR are allocated, the performance ofan STA having low performance is improved to meet QoS.

Here, Indices (or positions) of pilot tones allocated to each STA may beset in various manners.

As an embodiment, the AP may sequentially allocate pilot tones to STAsfrom the leftmost or rightmost pilot tone. For example, it is assumedthat 8 pilot tones are allocated to STAs 1 to 3. In this case, theleftmost first pilot tone may be allocated to STA 1, the second pilottone disposed to the right of the first pilot tone may be allocated toSTA 2, the third pilot tone disposed to the right of the second pilottone may be allocated to STA 3, and the fourth pilot tone disposed tothe right of the third pilot tone may be allocated to STA 1.Consequently, the first, fourth and seventh pilot tones are allocated toSTA 1, the second, fifth and eighth pilot tones are allocated to STA 2and the third and sixth pilot tones are allocated to STA 3.

As another embodiment, the AP may sequentially allocate pilot tones toSTAs from the leftmost or rightmost pilot tones by the number of pilottones allocated per STA.

For example, it is assumed that 3 pilot tones are allocated to STA 1, 3pilot tones are allocated to STA 2 and 2 pilot tones are allocated toSTA 3. In this case, the 8 pilot tones may be allocated from theleftmost (or rightmost) pilot tones in such a manner that 3, 3, and 2pilot tones are sequentially respectively allocated to STAs 1, 2 and 3.Consequently, first to third pilot tones are allocated to STA 1, thefourth to sixth pilot tones are allocated to STA2 and the seventh andeighth pilot tones are allocated to STA 3. Here, the first pilot tonemay refer to the leftmost or rightmost pilot tone from among pilot tonesin the frequency band.

As another embodiment, a situation will be described in which STA 1 andSTA 2 perform UL MU transmission using one stream and a 20 MHz bandwidthis allocated thereto. Here, the number, indices and values of pilottones applied to the 20 MHz bandwidth may conform to the scheme proposedin the first embodiment. The number of pilot tones allocated to each STAmay be determined in proportion to an SINR ratio. When the SINR ratio ofSTA 1 to STA 2 is 1:4, 2 (rounding off 1.6) pilot tones are allocated toSTA 1 and 6 pilot tones are allocated to STA 2. Here, the first andsecond pilot tones may be allocated to STA 1 and the fourth to eighthpilot tones may be sequentially allocated to STA 2 according to theabove description. Accordingly, values of the pilot tones allocated tothe STAs may be determined as shown in FIG. 33(c). In FIG. 33(c), iSTSindicates a stream index and ψ^(NSTB,8) _(iSTS,j) indicates a value of apilot tone at a j-th position from among 8 pilot tones in a streamhaving iSTS.

When there is a large number of STAs that need to be allocated pilottones in a situation where the number of pilot tones is limited, thenumber of pilot tones that may be allocated to each STA decreases whenthe above-described embodiment is applied, remarkably deteriorating CFOestimation performance. Accordingly, a method of grouping STAs andallocating pilot tones to each group is proposed to increase the numberof pilot tones allocated to each STA.

Here, STAs may be grouped according to the following embodiment.

1) A maximum number NU_max of STAs that may belong to one group and analpha value that is a channel orthogonality threshold (0 to 1:orthogonality increases as the alpha value decreases) are set.

2) STAs are sorted in descending order of SINR.

3) Correlation values between a channel of an STA having the highestSINR and channels of other STAs are obtained and the maximum numberNU_max of STAs from an STA having the smallest correlation value fromamong STAs having correlation values less than the alpha value aregrouped.

4) Steps 1) to 3) are sequentially performed for ungrouped STAs from anSTA having the highest SINR until all STAs are grouped. Here, one groupmay include one STA.

STAs belonging to each group use pilot tones allocated to each group.For example, STA 1 and STA 2 may belong to a first group and 4 pilottones may be allocated to the first group. In this case, STA 1 and STA 2may use the 4 pilot tones allocated to the first group. Here, the methodof allocating pilot tones per group may be applied by replacing an STAby a group in the above-described embodiments. In this case, the averageSINR of STAs in a group may be used as an SINR.

FIG. 34 is a flowchart illustrating a data transmission method of an STAdevice according to an embodiment of the present invention. Theabove-described embodiments may be equally applied in relation to theflowchart. Accordingly, redundant description will be omittedhereinafter.

Referring to FIG. 34, an STA may generate a PPDU (S3401). Here, thegenerated PPDU includes a physical preamble and a data field.

Then, the STA may transmit the generated PPDU (S3402). Here, the datafiled may be transmitted using a 106-tone resource unit including firstto fourth pilot tones. Here, the positions of the first to fourth pilottones may correspond to positions of 4 pilot tones from among 8 pilottones included in 4 26-tone resource units at positions corresponding tothe 106-tone resource unit. Otherwise, the positions of the first tofourth pilot tones may correspond to positions of 4 pilot tones fromamong 8 pilot tones included in 2 26-tone resource units at positionscorresponding to the 106-tone resource unit. This has been describedabove with reference to FIG. 32 in the fortieth embodiment and thusredundant description is omitted.

FIG. 35 is a block diagram of each STA device according to an embodimentof the present invention.

In FIG. 35, an STA device 3510 may include a memory 3512, a processor3511 and an RF unit 3513. And, as described above, the STA device may bean AP or a non-AP STA as an HE STA device.

The RF unit 3513 may transmit/receive a radio signal with beingconnected to the processor 3511. The RF unit 3513 may transmit a signalby up-converting the data received from the processor 3511 to thetransmission/reception band.

The processor 3511 may implement the physical layer and/or the MAC layeraccording to the IEEE 802.11 system with being connected to the RF unit4013. The processor 3511 may be constructed to perform the operationaccording to the various embodiments of the present invention accordingto the drawings and description. In addition, the module forimplementing the operation of the STA 3510 according to the variousembodiments of the present invention described above may be stored inthe memory 3512 and executed by the processor 3511.

The memory 3512 is connected to the processor 3511, and stores varioustypes of information for executing the processor 3511. The memory 3512may be included interior of the processor 3511 or installed exterior ofthe processor 3511, and may be connected with the processor 3511 by awell known means.

In addition, the STA device 3510 may include a single antenna or amultiple antenna.

The detailed construction of the STA device 3510 of FIG. 35 may beimplemented such that the description of the various embodiments of thepresent invention is independently applied or two or more embodimentsare simultaneously applied.

Although the description of the present invention is explained withreference to each of the accompanying drawings for clarity, it ispossible to design new embodiments by merging the embodiments shown inthe accompanying drawings with each other. Further, a display device maybe non-limited by the configurations and methods of the embodimentsmentioned in the foregoing description. The embodiments mentioned in theforegoing description may be configured in a manner of being selectivelycombined with one another entirely or in part to enable variousmodifications.

It will be appreciated by those skilled in the art that variousmodifications and variations may be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

Mode for Invention

Various embodiments have been described in the best mode for carryingout the invention.

INDUSTRIAL APPLICABILITY

While the data transmission and reception methods in a wirelesscommunication system according to the present invention have beendescribed on the basis of examples in which the methods are applied toIEEE 802.11, the methods are applicable to various wirelesscommunication systems in addition to IEEE 802.11.

The invention claimed is:
 1. A data transmission method of a station(STA) in a wireless local area network (WLAN) system, comprising:generating a physical protocol data unit (PPDU) including a physicalpreamble and a data field; and transmitting the PPDU, wherein, when afirst data field is transmitted within a specific bandwidth, at leasttwo 106-tone resource units are included in the specific bandwidth, whenthe two 106-tone resource units include first to fourth pilot tonesrespectively and 106 tones included in the 106-tone resource unit arepositioned at indices 0 to 105 sequentially: wherein, in one 106-toneresource unit, the first pilot tone is positioned at the index 6, thesecond pilot tone is positioned at the index 32, the third pilot tone ispositioned at the index 74, and the fourth pilot tone is positioned atthe index 100, and wherein, in another 106-tone resource unit, the firstpilot tone is positioned at the index 5, the second pilot tone ispositioned at the index 31, the third pilot tone is positioned at theindex 73, and the fourth pilot tone is positioned at the index
 99. 2.The data transmission method according to claim 1, when the specificbandwidth is a 20 MHz bandwidth: wherein the 20 MHz includes 6 leftguard tones, a first 106-tone resource unit, a first 13-tone resourceunit, 7 DC (Direct Current) tones, a second 13-tone resource unit, asecond 106-tone resource unit and 5 right guard tones, sequentially,when an index 0 is allocated to a central DC tone among the 7 DC tones,indices from +1 to +127 are sequentially allocated to tones located on aright side of the central DC tone in a right direction, and indices −1to −128 are sequentially allocated to tones located on a left side ofthe central DC tone in a left direction: wherein, in the first 106-toneresource unit, the first pilot tone is positioned at the index −116, thesecond pilot tone is positioned at the index −90, the third pilot toneis positioned at the index −48, and the fourth pilot tone is positionedat the index −22, and wherein, in the second 106-tone resource unit, thefirst pilot tone is positioned at the index +22, the second pilot toneis positioned at the index +48, the third pilot tone is positioned atthe index +90, and the fourth pilot tone is positioned at the index+116.
 3. The data transmission method according to claim 2, wherein thefirst 106-tone resource unit is the one 106-tone resource unit, and thesecond 106-tone resource unit is the another 106-tone resource unit. 4.The data transmission method according to claim 1, when the specificbandwidth is a 40 MHz bandwidth: wherein the 40 MHz includes 12 leftguard tones, 1 leftover tone, a first 106-tone resource unit, 1 leftovertone, a first 26-tone resource unit, 1 leftover tone, a second 106-toneresource unit, 1 leftover tone, 5 DC (Direct Current) tones, 1 leftovertone, a third 106-tone resource unit, 1 leftover tone, a second 26-toneresource unit, 1 leftover tone, a fourth 106-tone resource unit, 1leftover tone, and 11 right guard tones, sequentially, when an index 0is allocated to a central DC tone among the 5 DC tones, indices +1to+255 are sequentially allocated to tones located on a right side ofthe central DC tone in a right direction, and indices −1 to −256 aresequentially allocated to tones located on a left side of the central DCtone in a left direction: wherein, in the first 106-tone resource unit,the first pilot tone is positioned at the index −238, the second pilottone is positioned at the index −212, the third pilot tone is positionedat the index −170, and the fourth pilot tone is positioned at the index−144, wherein, in the second 106-tone resource unit, the first pilottone is positioned at the index −104, the second pilot tone ispositioned at the index −78, the third pilot tone is positioned at theindex −36, and the fourth pilot tone is positioned at the index −10,wherein, in the third 106-tone resource unit, the first pilot tone ispositioned at the index +10, the second pilot tone is positioned at theindex +36, the third pilot tone is positioned at the index +78, and thefourth pilot tone is positioned at the index +104, and wherein, in thefourth 106-tone resource unit, the first pilot tone is positioned at theindex +144, the second pilot tone is positioned at the index +170, thethird pilot tone is positioned at the index +212, and the fourth pilottone is positioned at the index +238.
 5. The data transmission methodaccording to claim 4, wherein the first and the second 106-tone resourceunits are the another 106-tone resource unit, and the third and thefourth 106-tone resource units are the one 106-tone resource unit. 6.The data transmission method according to claim 1, when the specificbandwidth is a 80 MHz bandwidth: wherein the 80 MHz includes 12 leftguard tones, 1 leftover tone, a first 106-tone resource unit, 1 leftovertone, a first 26-tone resource unit, 1 leftover tone, a second 106-toneresource unit, 2 leftover tones, a third 106-tone resource unit, 1leftover tone, a second 26-tone resource unit, 1 leftover tone, a fourth106-tone resource unit, 1 leftover tone, a first 13-tone resource unit,7 DC (Direct Current) tones, a second 13-tone resource unit, 1 leftovertone, a fifth 106-tone resource unit, 1 leftover tone, a third 26-toneresource unit, 1 leftover tone, a sixth 106-tone resource unit, 2leftover tones, a seventh 106-tone resource unit, 1 leftover tone, afourth 26-tone resource unit, 1 leftover tone, a eighth 106-toneresource unit, 1 leftover tone, and 11 right guard tones, sequentially,when an index 0 is allocated to a central DC tone among the 5 DC tones,indices +1 to +511 are sequentially allocated to tones located on aright side of the central DC tone in a right direction, and indices −1to −512 are sequentially allocated to tones located on a left side ofthe central DC tone in a left direction: wherein, in the first 106-toneresource unit, the first pilot tone is positioned at the index −494, thesecond pilot tone is positioned at the index −468, the third pilot toneis positioned at the index −426, and the fourth pilot tone is positionedat the index −400, wherein, in the second 106-tone resource unit, thefirst pilot tone is positioned at the index −360, the second pilot toneis positioned at the index −334, the third pilot tone is positioned atthe index −292, and the fourth pilot tone is positioned at the index−266, wherein, in the third 106-tone resource unit, the first pilot toneis positioned at the index −252, the second pilot tone is positioned atthe index −226, the third pilot tone is positioned at the index −184,and the fourth pilot tone is positioned at the index −158, wherein, inthe fourth 106-tone resource unit, the first pilot tone is positioned atthe index −118, the second pilot tone is positioned at the index −92,the third pilot tone is positioned at the index −50, and the fourthpilot tone is positioned at the index −24, wherein, in the fifth106-tone resource unit, the first pilot tone is positioned at the index+24, the second pilot tone is positioned at the index +50, the thirdpilot tone is positioned at the index +92, and the fourth pilot tone ispositioned at the index +118, wherein, in the sixth 106-tone resourceunit, the first pilot tone is positioned at the index +158, the secondpilot tone is positioned at the index +184, the third pilot tone ispositioned at the index +226, and the fourth pilot tone is positioned atthe index +252, wherein, in the seventh 106-tone resource unit, thefirst pilot tone is positioned at the index +266, the second pilot toneis positioned at the index +292, the third pilot tone is positioned atthe index +334, and the fourth pilot tone is positioned at the index+360, and wherein, in the eighth 106-tone resource unit, the first pilottone is positioned at the index +400, the second pilot tone ispositioned at the index +426, the third pilot tone is positioned at theindex +468, and the fourth pilot tone is positioned at the index +494.7. The data transmission method according to claim 6, wherein the firstto the fourth 106-tone resource units are the another 106-tone resourceunit, and the fifth to the eighth 106-tone resource units are the one106-tone resource unit.
 8. The data transmission method according toclaim 1, wherein a first pilot sequence {1 1 1 −1} is applied for thefirst to fourth pilot tones.
 9. The data transmission method accordingto claim 1, wherein, when a second data field is transmitted using a996-tone resource unit including first to sixteenth pilot tones, asecond pilot sequence {1 1 1 −1 −1 1 1 1 1 1 1 −1 −1 1 1 1} is appliedfor the first to sixteenth pilot tones.
 10. The data transmission methodaccording to claim 1, wherein the two 106-tone resource units aresymmetrically located with DC tones as a center in the specificbandwidth.
 11. A station (STA) in a wireless local area network (WLAN)system, comprising: an RF unit configured to transmit and receive RFsignals; and a processor configured to control the RF unit, wherein theprocessor is further configured to generate a physical protocol dataunit (PPDU) including a physical preamble and a data field and totransmit the PPDU, wherein, when a first data field is transmittedwithin a specific bandwidth, at least two 106-tone resource units areincluded in the specific bandwidth, when the two 106-tone resource unitsinclude first to fourth pilot tones respectively and 106 tones includedin the 106-tone resource unit are positioned at indices 0 to 105sequentially: wherein, in one 106-tone resource unit, the first pilottone is positioned at the index 6, the second pilot tone is positionedat the index 32, the third pilot tone is positioned at the index 74, andthe fourth pilot tone is positioned at the index 100, and wherein, inanother 106-tone resource unit, the first pilot tone is positioned atthe index 5, the second pilot tone is positioned at the index 31, thethird pilot tone is positioned at the index 73, and the fourth pilottone is positioned at the index
 99. 12. The STA according to claim 11,wherein the first to fourth pilot tones in the one 106-tone resourceunit and the first to fourth pilot tones in the another 106-toneresource unit are symmetrically located with DC tones as a center in thespecific bandwidth.
 13. The STA according to claim 11, when the specificbandwidth is a 20 MHz bandwidth: wherein the 20 MHz includes 6 leftguard tones, a first 106-tone resource unit, a first 13-tone resourceunit, 7 DC (Direct Current) tones, a second 13-tone resource unit, asecond 106-tone resource unit and 5 right guard tones, sequentially,when an index 0 is allocated to a central DC tone among the 7 DC tones,indices from +1 to +127 are sequentially allocated to tones located on aright side of the central DC tone in a right direction, and indices −1to −128 are sequentially allocated to tones located on a left side ofthe central DC tone in a left direction: wherein, in the first 106-toneresource unit, the first pilot tone is positioned at the index −116, thesecond pilot tone is positioned at the index −90, the third pilot toneis positioned at the index −48, and the fourth pilot tone is positionedat the index −22, and wherein, in the second 106-tone resource unit, thefirst pilot tone is positioned at the index +22, the second pilot toneis positioned at the index +48, the third pilot tone is positioned atthe index +90, and the fourth pilot tone is positioned at the index+116.
 14. The STA according to claim 13, wherein the first 106-toneresource unit is the one 106-tone resource unit, and the second 106-toneresource unit is the another 106-tone resource unit.
 15. The STAaccording to claim 11, when the specific bandwidth is a 40 MHzbandwidth: wherein the 40 MHz includes 12 left guard tones, 1 leftovertone, a first 106-tone resource unit, 1 leftover tone, a first 26-toneresource unit, 1 leftover tone, a second 106-tone resource unit, 1leftover tone, 5 DC (Direct Current) tones, 1 leftover tone, a third106-tone resource unit, 1 leftover tone, a second 26-tone resource unit,1 leftover tone, a fourth 106-tone resource unit, 1 leftover tone, and11 right guard tones, sequentially, when an index 0 is allocated to acentral DC tone among the 5 DC tones, indices +1 to +255 aresequentially allocated to tones located on a right side of the centralDC tone in a right direction, and indices −1 to −256 are sequentiallyallocated to tones located on a left side of the central DC tone in aleft direction: wherein, in the first 106-tone resource unit, the firstpilot tone is positioned at the index −238, the second pilot tone ispositioned at the index −212, the third pilot tone is positioned at theindex −170, and the fourth pilot tone is positioned at the index −144,wherein, in the second 106-tone resource unit, the first pilot tone ispositioned at the index −104, the second pilot tone is positioned at theindex −78, the third pilot tone is positioned at the index −36, and thefourth pilot tone is positioned at the index −10, wherein, in the third106-tone resource unit, the first pilot tone is positioned at the index+10, the second pilot tone is positioned at the index +36, the thirdpilot tone is positioned at the index +78, and the fourth pilot tone ispositioned at the index +104, and wherein, in the fourth 106-toneresource unit, the first pilot tone is positioned at the index +144, thesecond pilot tone is positioned at the index +170, the third pilot toneis positioned at the index +212, and the fourth pilot tone is positionedat the index +238.
 16. The STA according to claim 15, wherein the firstand the second 106-tone resource units are the another 106-tone resourceunit, and the third and the fourth 106-tone resource units are the one106-tone resource unit.
 17. The STA according to claim 11, when thespecific bandwidth is a 80 MHz bandwidth: wherein the 80 MHz includes 12left guard tones, 1 leftover tone, a first 106-tone resource unit, 1leftover tone, a first 26-tone resource unit, 1 leftover tone, a second106-tone resource unit, 2 leftover tones, a third 106-tone resourceunit, 1 leftover tone, a second 26-tone resource unit, 1 leftover tone,a fourth 106-tone resource unit, 1 leftover tone, a first 13-toneresource unit, 7 DC (Direct Current) tones, a second 13-tone resourceunit, 1 leftover tone, a fifth 106-tone resource unit, 1 leftover tone,a third 26-tone resource unit, 1 leftover tone, a sixth 106-toneresource unit, 2 leftover tones, a seventh 106-tone resource unit, 1leftover tone, a fourth 26-tone resource unit, 1 leftover tone, a eighth106-tone resource unit, 1 leftover tone, and 11 right guard tones,sequentially, when an index 0 is allocated to a central DC tone amongthe 5 DC tones, indices +1 to +511 are sequentially allocated to toneslocated on a right side of the central DC tone in a right direction, andindices −1 to −512 are sequentially allocated to tones located on a leftside of the central DC tone in a left direction: wherein, in the first106-tone resource unit, the first pilot tone is positioned at the index−494, the second pilot tone is positioned at the index −468, the thirdpilot tone is positioned at the index −426, and the fourth pilot tone ispositioned at the index −400, wherein, in the second 106-tone resourceunit, the first pilot tone is positioned at the index −360, the secondpilot tone is positioned at the index −334, the third pilot tone ispositioned at the index −292, and the fourth pilot tone is positioned atthe index −266, wherein, in the third 106-tone resource unit, the firstpilot tone is positioned at the index −252, the second pilot tone ispositioned at the index −226, the third pilot tone is positioned at theindex −184, and the fourth pilot tone is positioned at the index −158,wherein, in the fourth 106-tone resource unit, the first pilot tone ispositioned at the index −118, the second pilot tone is positioned at theindex −92, the third pilot tone is positioned at the index −50, and thefourth pilot tone is positioned at the index −24, wherein, in the fifth106-tone resource unit, the first pilot tone is positioned at the index+24, the second pilot tone is positioned at the index +50, the thirdpilot tone is positioned at the index +92, and the fourth pilot tone ispositioned at the index +118, wherein, in the sixth 106-tone resourceunit, the first pilot tone is positioned at the index +158, the secondpilot tone is positioned at the index +184, the third pilot tone ispositioned at the index +226, and the fourth pilot tone is positioned atthe index +252, wherein, in the seventh 106-tone resource unit, thefirst pilot tone is positioned at the index +266, the second pilot toneis positioned at the index +292, the third pilot tone is positioned atthe index +334, and the fourth pilot tone is positioned at the index+360, and wherein, in the eighth 106-tone resource unit, the first pilottone is positioned at the index +400, the second pilot tone ispositioned at the index +426, the third pilot tone is positioned at theindex +468, and the fourth pilot tone is positioned at the index +494.18. The STA according to claim 17, wherein the first to the fourth106-tone resource units are the another 106-tone resource unit, and thefifth to the eighth 106-tone resource units are the one 106-toneresource unit.
 19. The STA according to claim 11, wherein a first pilotsequence {1 1 1 −1} is applied for the first to fourth pilot tones, andwherein, when a second data field is transmitted using a 996-toneresource unit including first to sixteenth pilot tones, a second pilotsequence {1 1 1 −1 −1 1 1 1 1 1 1 −1 −1 1 1 1} is applied for the firstto sixteenth pilot tones.
 20. A data transmission method of an accesspoint (AP) in a wireless local area network (WLAN) system, comprising:generating a physical protocol data unit (PPDU) including a physicalpreamble and a data field; and transmitting the PPDU, wherein, when thedata field is transmitted within a specific bandwidth, at least two106-tone resource units are included in the specific bandwidth, when thetwo 106-tone resource units include first to fourth pilot tonesrespectively and 106 tones included in the 106-tone resource unit arepositioned at indices 0 to 105 sequentially: wherein, in one 106-toneresource unit, the first pilot tone is positioned at the index 6, thesecond pilot tone is positioned at the index 32, the third pilot tone ispositioned at the index 74, and the fourth pilot tone is positioned atthe index 100, and wherein, in another 106-tone resource unit, the firstpilot tone is positioned at the index 5, the second pilot tone ispositioned at the index 31, the third pilot tone is positioned at theindex 73, and the fourth pilot tone is positioned at the index 99.